# List of U.S. county name etymologies (J–M)

This is a list of U.S. county name etymologies, covering the letters J to M.

## J

| County name | State | Name origin |
| Jack County | Texas | Patrick Churchill Jack and his brother William Houston Jack, both soldiers of the Texas Revolution |
| Jackson County | Alabama | Andrew Jackson, the seventh president of the United States |
| Jackson County | Arkansas | Andrew Jackson, the seventh president of the United States |
| Jackson County | Colorado | Andrew Jackson, the seventh president of the United States |
| Jackson County | Florida | Andrew Jackson, the seventh president of the United States |
| Jackson County | Illinois | Andrew Jackson, the seventh president of the United States |
| Jackson County | Indiana | Andrew Jackson, the seventh president of the United States |
| Jackson County | Iowa | Andrew Jackson, the seventh president of the United States |
| Jackson County | Kansas | Andrew Jackson, the seventh president of the United States |
| Jackson County | Kentucky | Andrew Jackson, the seventh president of the United States |
| Jackson County | Michigan | Andrew Jackson, the seventh president of the United States |
| Jackson County | Minnesota | Andrew Jackson, the seventh president of the United States |
| Jackson County | Mississippi | Andrew Jackson, the seventh president of the United States |
| Jackson County | Missouri | Andrew Jackson, the seventh president of the United States |
| Jackson County | North Carolina | Andrew Jackson, the seventh president of the United States |
| Jackson County | Ohio | Andrew Jackson, the seventh president of the United States |
| Jackson County | Oklahoma | Andrew Jackson, the seventh president of the United States |
| Jackson County | Oregon | Andrew Jackson, the seventh president of the United States |
| Jackson County | Tennessee | Andrew Jackson, the seventh president of the United States |
| Jackson County | Texas | Andrew Jackson, the seventh president of the United States |
| Jackson County | West Virginia | Andrew Jackson, the seventh president of the United States |
| Jackson County | Wisconsin | Andrew Jackson, the seventh president of the United States |
| Jackson Parish | Louisiana | Andrew Jackson, the seventh president of the United States |
| Jackson County | Georgia | James Jackson, a U.S. Congressman and the 23rd Governor of Georgia |
| Jackson County | South Dakota | J.R. Jackson, a legislator of the Dakota Territory |
| James City County | Virginia | Named for James City (Virginia Company) (one of four incorporations of the Virginia Colony), itself named for James I of England by his son, King Charles I |
| Jasper County | Georgia | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Illinois | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Indiana | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Iowa | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Mississippi | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Missouri | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | South Carolina | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jasper County | Texas | William Jasper, a hero of the Battle of Sullivan's Island during the American Revolutionary War |
| Jay County | Indiana | John Jay, the first U.S. Secretary of State and first Chief Justice of the Supreme Court |
| Jeff Davis County | Georgia | Jefferson Davis, president of the Confederate States |
| Jeff Davis County | Texas | Jefferson Davis, president of the Confederate States |
| Jefferson County | Alabama | Thomas Jefferson, the third president of the United States |
| Jefferson County | Arkansas | Thomas Jefferson, the third president of the United States |
| Jefferson County | Florida | Thomas Jefferson, the third president of the United States |
| Jefferson County | Georgia | Thomas Jefferson, the third president of the United States |
| Jefferson County | Idaho | Thomas Jefferson, the third president of the United States |
| Jefferson County | Illinois | Thomas Jefferson, the third president of the United States |
| Jefferson County | Indiana | Thomas Jefferson, the third president of the United States |
| Jefferson County | Iowa | Thomas Jefferson, the third president of the United States |
| Jefferson County | Kansas | Thomas Jefferson, the third president of the United States |
| Jefferson County | Kentucky | Thomas Jefferson, the third president of the United States |
| Jefferson County | Mississippi | Thomas Jefferson, the third president of the United States |
| Jefferson County | Missouri | Thomas Jefferson, the third president of the United States |
| Jefferson County | Montana | Thomas Jefferson, the third president of the United States |
| Jefferson County | Nebraska | Thomas Jefferson, the third president of the United States |
| Jefferson County | New York | Thomas Jefferson, the third president of the United States |
| Jefferson County | Ohio | Thomas Jefferson, the third president of the United States |
| Jefferson County | Oklahoma | Thomas Jefferson, the third president of the United States |
| Jefferson County | Oregon | Thomas Jefferson, the third president of the United States |
| Jefferson County | Pennsylvania | Thomas Jefferson, the third president of the United States |
| Jefferson County | Tennessee | Thomas Jefferson, the third president of the United States |
| Jefferson County | Texas | Thomas Jefferson, the third president of the United States |
| Jefferson County | Washington | Thomas Jefferson, the third president of the United States |
| Jefferson County | West Virginia | Thomas Jefferson, the third president of the United States |
| Jefferson County | Wisconsin | Thomas Jefferson, the third president of the United States |
| Jefferson Parish | Louisiana | Thomas Jefferson, the third president of the United States |
| Jefferson County | Colorado | Named for the extralegal Jefferson Territory (itself named for U.S. President Thomas Jefferson), of which the county was a part from 1859 to 1861 |
| Jefferson Davis County | Mississippi | Jefferson Davis, president of the Confederate States |
| Jefferson Davis Parish | Louisiana | Jefferson Davis, president of the Confederate States |
| Jenkins County | Georgia | Charles Jones Jenkins, the 44th Governor of Georgia |
| Jennings County | Indiana | Jonathan Jennings, the first Governor of Indiana |
| Jerauld County | South Dakota | H.A. Jerauld, a legislator of the Dakota Territory |
| Jerome County | Idaho | Named for the town of Jerome, Idaho, named in turn for Jerome Hill, an investor in the North Side Twin Falls Canal Company. |
| Jersey County | Illinois | The U.S. state of New Jersey |
| Jessamine County | Kentucky | Named for Jessamine Creek, so called because of the jasmine plants that grow next to it. |
| Jewell County | Kansas | Colonel Lewis R. Jewell of the Sixth Kansas Cavalry Regiment |
| Jim Hogg County | Texas | James Hogg, the 20th Governor of Texas |
| Jim Wells County | Texas | James B. Wells Jr., a judge and Democratic boss in South Texas |
| Jo Daviess County | Illinois | Joseph Hamilton Daveiss, a soldier killed at the Battle of Tippecanoe |
| Johnson County | Arkansas | Ben Johnson, a judge in the Arkansas Territory |
| Johnson County | Georgia | Herschel Vespasian Johnson, a U.S. Senator and the 41st Governor of Georgia |
| Johnson County | Illinois | Richard Mentor Johnson, a U.S. Congressman and the 9th Vice President of the United States |
| Johnson County | Iowa | Richard Mentor Johnson, a U.S. Congressman and the 9th Vice President of the United States |
| Johnson County | Kentucky | Richard Mentor Johnson, a U.S. Congressman and the 9th Vice President of the United States |
| Johnson County | Missouri | Richard Mentor Johnson, a U.S. Congressman and the 9th Vice President of the United States |
| Johnson County | Nebraska | Richard Mentor Johnson, a U.S. Congressman and the 9th Vice President of the United States |
| Johnson County | Indiana | John Johnson, a judge of the Indiana Supreme Court |
| Johnson County | Kansas | Thomas Johnson, an early Methodist missionary to the Shawnee tribe in Kansas |
| Johnson County | Tennessee | Thomas Johnson, an early settler of the area |
| Johnson County | Texas | Middleton Johnson, a Texas Ranger, soldier, and politician |
| Johnson County | Wyoming | E. P. Johnson, a Cheyenne attorney |
| Johnston County | North Carolina | Gabriel Johnston, the 6th Colonial Governor of North Carolina |
| Johnston County | Oklahoma | Douglas H. Johnston, the last governor of the Chickasaw Nation |
| Jones County | Georgia | James Jones, a U.S. Representative from Georgia |
| Jones County | Iowa | George Wallace Jones, one of the first two U.S. senators to represent Iowa |
| Jones County | South Dakota | George Wallace Jones, one of the first two U.S. senators to represent Iowa |
| Jones County | Mississippi | John Paul Jones, commander of the Continental Navy during the American Revolutionary War |
| Jones County | North Carolina | Willie Jones, a Revolutionary leader and president of the North Carolina Council of Safety |
| Jones County | Texas | Anson Jones, the last President of the Republic of Texas |
| Josephine County | Oregon | Named for a creek, itself probably named after Virginia Josephine Rollins Ort |
| Juab County | Utah | A Ute word meaning "valley" or "plain" |
| Judith Basin County | Montana | Named by explorer William Clark for his future wife, Julia "Judith" Hancock |
| Juneau County | Wisconsin | Solomon Juneau, a French-Canadian trader who helped found and was the first mayor of Milwaukee |
| Juneau City and Borough | Alaska | Joseph Juneau, a Canadian gold prospector who co-founded the city of Juneau |
| Juniata County | Pennsylvania | An Iroquoian word, onayutta, meaning "standing stone" |

## K

| County name | State | Name origin |
| Kalamazoo County | Michigan | The Kalamazoo River which runs through it, itself of uncertain origin: see Etymology of Kalamazoo |
| Kalawao County | Hawaii | Hawaiian kalawao, "mountain-side wild woods." |
| Kalkaska County | Michigan | A word invented by Henry Schoolcraft, whose family name was Calcraft; the "K"s may have been added to make the name appear more like a Native American word |
| Kanabec County | Minnesota | The Snake River which runs through it, itself named for an Ojibwe word, Ginebig, meaning "snake" |
| Kanawha County | West Virginia | The Kanawha River which runs through it, itself named for an Iroquoian word, ka(ih)nawha, meaning "waterway" or "canoe way" |
| Kandiyohi County | Minnesota | Dakota name for several lakes, meaning "where the buffalo fish come" |
| Kane County | Illinois | Elias Kane, a U.S. Senator and the first Illinois Secretary of State |
| Kane County | Utah | Thomas L. Kane, a Union general during the American Civil War and an influential supporter of the Latter-day Saint movement |
| Kankakee County | Illinois | A Miami Indian word, teeyaahkiki, meaning "open country" |
| Karnes County | Texas | Henry Karnes, a soldier of the Texas Revolution |
| Kauaʻi County | Hawaii | Its largest island, Kauaʻi, itself named for a son of the legendary discoverer of the Hawaiʻian Islands and possibly meaning "place around the neck" or "food season" |
| Kaufman County | Texas | David Spangler Kaufman, a legislator and diplomat of the Republic of Texas and later a U.S. Congressman |
| Kay County | Oklahoma | The letter "K", from its designation as "County K" before names were assigned |
| Kearney County | Nebraska | Fort Kearny, itself named for General Stephen Watts Kearny |
| Kearny County | Kansas | Stephen Watts Kearny, a general of the U.S. Army active on the American frontier during the Mexican–American War |
| Keith County | Nebraska | M. C. Keith, a local rancher |
| Kemper County | Mississippi | Reuben Kemper, an early settler of the area who rebelled against Spanish rule in Spanish West Florida |
| Kenai Peninsula Borough | Alaska | Kenai Peninsula, a headland named for the Athabascan people, Kahtnuht’ana Dena’ina ("People along the Kahtnu (Kenai River)"). |
| Kendall County | Illinois | Amos Kendall, the editor of an influential Frankfort, Kentucky newspaper who served as the 8th U.S. Postmaster General and an important adviser to President Andrew Jackson |
| Kendall County | Texas | George Wilkins Kendall, a journalist and Mexican–American War correspondent |
| Kenedy County | Texas | Mifflin Kenedy, an early rancher and businessman in South Texas |
| Kennebec County | Maine | An Eastern Abenaki word, /kínipekʷ/, meaning "large body of still water" |
| Kenosha County | Wisconsin | A Chippewa word meaning "pickerel", a type of fish |
| Kent County | Delaware | Kent, a county in England |
| Kent County | Maryland | Kent, a county in England |
| Kent County | Rhode Island | Kent, a county in England |
| Kent County | Michigan | James Kent, a jurist who represented Michigan Territory in its dispute with Ohio over the Toledo Strip |
| Kent County | Texas | Andrew Kent, who died at the Battle of the Alamo during the Texas Revolution |
| Kenton County | Kentucky | Simon Kenton, a frontiersman and soldier in the Ohio River region |
| Keokuk County | Iowa | Keokuk, chief of the Sauk tribe |
| Kern County | California | Edward Kern, an artist and cartographer who accompanied General John C. Frémont's third and fourth expeditions to the Western United States |
| Kerr County | Texas | James Kerr, an early settler and legislator of the Republic of Texas |
| Kershaw County | South Carolina | Joseph B. Kershaw, a lawyer, South Carolina legislator, and Confederate general during the American Civil War |
| Ketchikan Gateway Borough | Alaska | Tlingit Kichx̱áan (Kitschk-hin), meaning "the river belonging to Kitschk" or "Thundering Wings of an Eagle." |
| Kewaunee County | Wisconsin | Disputed; probably a Chippewa term meaning either "prairie hen" or "I cross a point of land by boat" |
| Keweenaw County | Michigan | An Ojibwe word, kee-wi-wai-non-ing, which means "portage" or "place where portage is made" |
| Keya Paha County | Nebraska | Dakota language words Ké-ya Pa-há Wa-kpá, meaning "turtle hill river" |
| Kidder County | North Dakota | Jefferson Parish Kidder, a U.S. Congressman who represented the Dakota Territory |
| Kimball County | Nebraska | Thomas L. Kimball, an official of the Union Pacific Railroad |
| Kimble County | Texas | George C. Kimble, who died at the Battle of the Alamo during the Texas Revolution |
| King County | Texas | William Philip King, who died at the Battle of the Alamo during the Texas Revolution |
| King County | Washington | William Rufus King, a U.S. Congressman and the 13th Vice President of the United States; "renamed" in honor of Martin Luther King Jr. (no relation) in 2005 |
| King George County | Virginia | George I of Great Britain |
| King William | Virginia | William III of England |
| King and Queen County | Virginia | King William III of England and Queen Mary II of England |
| Kingfisher County | Oklahoma | Unknown; possibly for a local rancher named David King Fisher, a rancher named John Fisher, or two different settlers named King and Fisher; later given additional currency in association with the belted kingfisher bird |
| Kingman County | Kansas | Samuel A. Kingman, who was Chief Justice of Kansas at the time of its creation |
| Kings County | California | The Kings River, itself originally named Río de los Santos Reyes ("River of the Holy Kings") |
| Kings County | New York | King Charles II of England |
| Kingsbury County | South Dakota | George W. Kingsbury and T.A. Kingsbury, two brothers who were members of several territorial legislatures |
| Kinney County | Texas | Henry Lawrence Kinney, an early settler of Texas |
| Kiowa County | Colorado | The Kiowa people, a Native American tribe |
| Kiowa County | Kansas | The Kiowa people, a Native American tribe |
| Kiowa County | Oklahoma | The Kiowa people, a Native American tribe |
| Kit Carson County | Colorado | Kit Carson, a frontiersman, explorer, and U.S. Army officer active across much of the American frontier |
| Kitsap County | Washington | Chief Kitsap of the Suquamish tribe |
| Kittitas County | Washington | Unknown; probably a Yakama word with any of numerous different meanings |
| Kittson County | Minnesota | Norman Kittson, a Canadian fur trader, railroad entrepreneur, and mayor of St. Paul |
| Klamath County | Oregon | The Klamath people, a Native American tribe |
| Kleberg County | Texas | Robert J. Kleberg, an early settler and veteran of the Texas Revolution |
| Klickitat County | Washington | The Klickitat people, a Native American tribe |
| Knott County | Kentucky | James Proctor Knott, the 29th Governor of Kentucky |
| Knox County | Illinois | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Indiana | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Kentucky | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Maine | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Missouri | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Nebraska | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Ohio | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Tennessee | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Knox County | Texas | Henry Knox, a general during the American Revolutionary War and the first U.S. Secretary of War |
| Kodiak Island Borough | Alaska | Kodiak Island, from Alutiiq qikertaq, "island." |
| Koochiching County | Minnesota | An Ojibwe or Cree word meaning "at the place of inlets", referring to the nearby Rainy Lake and Rainy River |
| Kootenai County | Idaho | The Kootenay people, a Native American tribe |
| Kosciusko County | Indiana | Tadeusz Kościuszko, a Polish ally of the Americans during the Revolutionary War |
| Kossuth County | Iowa | Lajos Kossuth, the Governor-President of the Kingdom of Hungary during the Revolution of 1848 who went into exile in the United States |
| Kusilvak Census Area | Alaska | The Kusilvak Mountains |

## L

| County name | State | Name origin |
| La Crosse County | Wisconsin | Early explorer Zebulon Pike saw the Indians playing a game similar to Lacrosse, a French game called such because the rackets resembled a bishop's crozier. |
| LaMoure County | North Dakota | Named for Judson LaMoure of who served many terms in the Dakota and North Dakota legislatures |
| La Paz County | Arizona | Named for a ghost town within the county, itself named for the Spanish word meaning "peace" |
| La Plata County | Colorado | The La Plata Mountains, which were named by Spanish explorers of the Domínguez–Escalante expedition for their reputed silver ore; la plata is Spanish for "silver" |
| La Porte County | Indiana | French for "the door" or "the port" |
| LaSalle County | Illinois | René-Robert Cavelier, Sieur de La Salle, an early French explorer of the Mississippi River |
| La Salle County | Texas | René-Robert Cavelier, Sieur de La Salle, an early French explorer of the Mississippi River |
| La Salle Parish | Louisiana | René-Robert Cavelier, Sieur de La Salle, an early French explorer of the Mississippi River |
| Labette County | Kansas | LaBette Creek which runs through it, itself named for French-Canadian fur trapper Pierre LaBette, who settled near the creek's mouth |
| Lac qui Parle County | Minnesota | French for "lake that speaks" |
| Lackawanna County | Pennsylvania | Lenape word for "stream that forks" |
| Laclede County | Missouri | Pierre Laclède, a French fur trader who co-founded the city of St. Louis |
| Lafayette County | Arkansas | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafayette County | Florida | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafayette County | Mississippi | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafayette County | Missouri | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafayette County | Wisconsin | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafayette Parish | Louisiana | Gilbert du Motier, Marquis de Lafayette, a French general who played a major role in the American Revolutionary War |
| Lafourche Parish | Louisiana | Bayou Lafourche (French: "the fork") |
| Lagrange County | Indiana | Named for the home of the Marquis de Lafayette outside of Paris, France |
| Lake County | California | Clear Lake, which dominates the county |
| Lake County | Colorado | Twin Lakes, two mountain lakes (now a reservoir) located just south of Leadville |
| Lake County | Florida | Named for the large number of lakes within the county |
| Lake County | Oregon | Named for the large number of lakes within the county, including Lake Abert, Summer Lake, Hart Lake, and Goose Lake |
| Lake County | South Dakota | Named for the large number of lakes within the county |
| Lake County | Illinois | Named for its location on Lake Michigan |
| Lake County | Indiana | Named for its location on Lake Michigan |
| Lake County | Michigan | Named for the several small lakes within the county |
| Lake County | Minnesota | Named for its location on Lake Superior |
| Lake County | Montana | Flathead Lake, which dominates the county |
| Lake County | Ohio | Named for its location on Lake Erie |
| Lake County | Tennessee | Reelfoot Lake, the county's most significant geographic feature along with the Mississippi River |
| Lake and Peninsula Borough | Alaska | Iliamna Lake and the Alaska Peninsula |
| Lake of the Woods County | Minnesota | Lake of the Woods, which dominates the county |
| Lamar County | Alabama | Lucius Quintus Cincinnatus Lamar II, a U.S. Senator, Secretary of the Interior, and Supreme Court justice |
| Lamar County | Georgia | Lucius Quintus Cincinnatus Lamar II, a U.S. Senator, Secretary of the Interior, and Supreme Court justice |
| Lamar County | Mississippi | Lucius Quintus Cincinnatus Lamar II, a U.S. Senator, Secretary of the Interior, and Supreme Court justice |
| Lamar County | Texas | Mirabeau B. Lamar, the second President of the Republic of Texas |
| Lamb County | Texas | George A. Lamb, who died in the Battle of San Jacinto during the Texas Revolution |
| Lamoille County | Vermont | Undocumented; possibly a misspelling of the intended name of Lake Champlain, or the French la moelle, meaning "the marrow" |
| Lampasas County | Texas | Undocumented; possibly for the Lampasas River, the old Lampazos mission in Mexico, or the Spanish name for any of several plants in the vicinity |
| Lancaster County | Nebraska | Named after the cities of Lancaster, Pennsylvania and Lancaster, England |
| Lancaster County | Pennsylvania | Lancashire, a county in England |
| Lancaster County | South Carolina | Lancaster, Pennsylvania |
| Lancaster County | Virginia | Lancaster, Pennsylvania |
| Lander County | Nevada | Frederick W. Lander, the chief engineer of a federal wagon route through the area |
| Lane County | Kansas | James H. Lane, a leader of the Jayhawker abolitionist movement who served as one of the first U.S. senators from Kansas |
| Lane County | Oregon | Joseph Lane, the first Governor of the Oregon Territory |
| Langlade County | Wisconsin | Charles Langlade, a fur merchant and one of the first settlers of Wisconsin |
| Lanier County | Georgia | Sidney Lanier, a Georgia poet |
| Lapeer County | Michigan | From the French "la pierre", meaning "flint" or "flint stone" |
| Laramie County | Wyoming | Jacques La Ramee, a French-Canadian fur trader |
| Larimer County | Colorado | William Larimer Jr., the founder of Denver |
| LaRue County | Kentucky | John LaRue, an early settler of the area |
| Las Animas County | Colorado | The Purgatoire River, which was once known as the Río de las Animas Perdidas en Purgatorio, Spanish for "River of Souls Lost in Purgatory" |
| Lassen County | California | Peter Lassen, one of General John C. Frémont's guides |
| Latah County | Idaho | Nez Perce for "the place of pine trees and pestle" |
| Latimer County | Oklahoma | J.S. Latimer, a member of the Oklahoma Constitutional Convention |
| Lauderdale County | Alabama | Colonel James Lauderdale, who died during the first Battle of New Orleans |
| Lauderdale County | Mississippi | Colonel James Lauderdale, who died during the first Battle of New Orleans |
| Lauderdale County | Tennessee | Colonel James Lauderdale, who died during the first Battle of New Orleans |
| Laurel County | Kentucky | Named for the mountain laurel trees common in the area |
| Laurens County | Georgia | Colonel John Laurens, a soldier and statesman during the American Revolutionary War |
| Laurens County | South Carolina | Henry Laurens, president of the Continental Congress |
| Lavaca County | Texas | The Lavaca River, itself originally called Les Veches by early French explorers for the wild buffalo that grazed its banks, which was later translated to the Spanish La Vaca, meaning "the cattle" |
| Lawrence County | Alabama | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Arkansas | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Illinois | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Indiana | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Kentucky | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Mississippi | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Missouri | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Ohio | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Tennessee | James Lawrence, a captain in the United States Navy and hero of the War of 1812 |
| Lawrence County | Pennsylvania | USS Lawrence, Oliver Hazard Perry's original flagship at the Battle of Lake Erie during the War of 1812 |
| Lawrence County | South Dakota | "Colonel" John Lawrence, who came to the county as first treasurer after serving in the Dakota Territorial Legislature |
| Le Flore County | Oklahoma | A prominent local family of Choctaw/French descent |
| Le Sueur County | Minnesota | Pierre-Charles Le Sueur, a French explorer |
| Lea County | New Mexico | Joseph Calloway Lea, a captain in the U.S. Army and founder of the New Mexico Military Academy |
| Leake County | Mississippi | Walter Leake, the Governor of Mississippi |
| Leavenworth County | Kansas | Colonel Henry Leavenworth, who established the original Fort Leavenworth |
| Lebanon County | Pennsylvania | A Biblical name meaning "white mountain" |
| Lee County | Alabama | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | Arkansas | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | Florida | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | Mississippi | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | North Carolina | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | South Carolina | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | Texas | Robert E. Lee, the highest-ranking general of the Confederate States Army during the American Civil War |
| Lee County | Georgia | Richard Henry Lee, a Virginia statesman who proposed in the Continental Congress that the colonies declare themselves free and independent, leading to the Declaration of Independence |
| Lee County | Illinois | Richard Henry Lee, a Virginia statesman who proposed in the Continental Congress that the colonies declare themselves free and independent, leading to the Declaration of Independence |
| Lee County | Iowa | Uncertain; possibly Robert E. Lee, who surveyed the Des Moines Rapids; William Elliot Lee, a land dealer who owned an area of Iowa that included the future county; Marsh, Delevan & Lee of New York, who owned interests in the Half-Breed Tract; or Albert Miller Lea, who surveyed the interior of Iowa |
| Lee County | Kentucky | Uncertain; either Robert E. Lee or his father, General Light-Horse Harry Lee, the 9th Governor of Virginia |
| Lee County | Virginia | General Light-Horse Harry Lee, the 9th Governor of Virginia and father of Robert E. Lee |
| Leelanau County | Michigan | Invented by Henry Schoolcraft, who gave the name "Leelinau" to some Native American women in his stories |
| Leflore County | Mississippi | Greenwood LeFlore, a Choctaw leader |
| Lehigh County | Pennsylvania | Derived from the Delaware Indian term Lechauweki or Lechauwekink, meaning "where there are forks" |
| Lemhi County | Idaho | King Limhi, a figure in the Book of Mormon |
| Lenawee County | Michigan | Derived from either the Delaware leno or lenno or the Shawnee lenawai, meaning "man" |
| Lenoir County | North Carolina | William Lenoir, an officer in the American Revolutionary War |
| Leon County | Florida | Juan Ponce de León, a Spanish explorer |
| Leon County | Texas | Martín De León, the founder of Victoria, Texas |
| Leslie County | Kentucky | Preston H. Leslie, the 26th Governor of Kentucky |
| Letcher County | Kentucky | Robert P. Letcher, the 15th Governor of Kentucky |
| Levy County | Florida | David Levy Yulee, an industrialist and U.S. Senator |
| Lewis County | Idaho | Meriwether Lewis, a co-leader of the Lewis and Clark Expedition |
| Lewis County | Kentucky | Meriwether Lewis, a co-leader of the Lewis and Clark Expedition |
| Lewis County | Missouri | Meriwether Lewis, a co-leader of the Lewis and Clark Expedition |
| Lewis County | Tennessee | Meriwether Lewis, a co-leader of the Lewis and Clark Expedition |
| Lewis County | Washington | Meriwether Lewis, a co-leader of the Lewis and Clark Expedition |
| Lewis County | New York | Morgan Lewis, the third Governor of New York |
| Lewis County | West Virginia | Colonel Charles Lewis, a soldier and pioneer leader |
| Lewis and Clark County | Montana | Meriwether Lewis and William Clark, who undertook the first expedition across the interior of the United States to the Pacific coast |
| City of Lexington | Virginia | The Battle of Lexington, fought in Lexington, Massachusetts during the American Revolutionary War |
| Lexington County | South Carolina | The Battle of Lexington, fought in Lexington, Massachusetts during the American Revolutionary War |
| Liberty County | Florida | Named for the philosophical ideal |
| Liberty County | Georgia | Named for the philosophical ideal |
| Liberty County | Montana | Named for the philosophical ideal |
| Liberty County | Texas | Named for the philosophical ideal |
| Licking County | Ohio | The Licking River, the etymology of which is highly conjectural |
| Limestone County | Alabama | Limestone Creek, itself named for the fact that it flows over limestone bedrock |
| Limestone County | Texas | From the numerous limestone deposits in the area |
| Lincoln County | Arkansas | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Colorado | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Idaho | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Kansas | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Minnesota | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Mississippi | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Montana | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Nebraska | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Nevada | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | New Mexico | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Oklahoma | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Oregon | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Washington | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | West Virginia | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Wisconsin | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Wyoming | Abraham Lincoln, the 16th President of the United States |
| Lincoln Parish | Louisiana | Abraham Lincoln, the 16th President of the United States |
| Lincoln County | Georgia | Benjamin Lincoln, a leading general in the American Revolutionary War and the first U.S. Secretary of War |
| Lincoln County | Kentucky | Benjamin Lincoln, a leading general in the American Revolutionary War and the first U.S. Secretary of War |
| Lincoln County | Missouri | Benjamin Lincoln, a leading general in the American Revolutionary War and the first U.S. Secretary of War |
| Lincoln County | North Carolina | Benjamin Lincoln, a leading general in the American Revolutionary War and the first U.S. Secretary of War |
| Lincoln County | Tennessee | Benjamin Lincoln, a leading general in the American Revolutionary War and the first U.S. Secretary of War |
| Lincoln County | Maine | The city of Lincoln, England |
| Lincoln County | South Dakota | Named after Lincoln County, Maine |
| Linn County | Iowa | Lewis F. Linn, a U.S. Senator who represented Missouri |
| Linn County | Kansas | Lewis F. Linn, a U.S. Senator who represented Missouri |
| Linn County | Missouri | Lewis F. Linn, a U.S. Senator who represented Missouri |
| Linn County | Oregon | Lewis F. Linn, a U.S. Senator who represented Missouri |
| Lipscomb County | Texas | Abner Smith Lipscomb, a judge and Secretary of State of the Republic of Texas |
| Litchfield County | Connecticut | The city of Litchfield, England |
| Little River County | Arkansas | The Little River, which forms part of the county boundary |
| Live Oak County | Texas | The Texas live oak tree under which the petition for a new county was signed |
| Livingston County | Illinois | Edward Livingston, the 46th mayor of New York City, a U.S. Congressman and the 11th U.S. Secretary of State |
| Livingston County | Kentucky | Edward Livingston, the 46th mayor of New York City, a U.S. Congressman and the 11th U.S. Secretary of State |
| Livingston County | Michigan | Edward Livingston, the 46th mayor of New York City, a U.S. Congressman and the 11th U.S. Secretary of State |
| Livingston County | Missouri | Edward Livingston, the 46th mayor of New York City, a U.S. Congressman and the 11th U.S. Secretary of State |
| Livingston Parish | Louisiana | Edward Livingston, the 46th mayor of New York City, a U.S. Congressman and the 11th U.S. Secretary of State |
| Livingston County | New York | Robert R. Livingston, one of the drafters of the Declaration of Independence and the first Chancellor of New York |
| Llano County | Texas | The Llano River, itself named for the Spanish llano, meaning "plains" |
| Logan County | Arkansas | |
| Logan County | Colorado | John A. Logan, a U.S. Congressman and Union general during the American Civil War |
| Logan County | Kansas | John A. Logan, a U.S. Congressman and Union general during the American Civil War |
| Logan County | Nebraska | John A. Logan, a U.S. Congressman and Union general during the American Civil War |
| Logan County | North Dakota | John A. Logan, a U.S. Congressman and Union general during the American Civil War |
| Logan County | Oklahoma | John A. Logan, a U.S. Congressman and Union general during the American Civil War |
| Logan County | Illinois | Dr. John Logan, a pioneer physician and father of General John A. Logan |
| Logan County | Kentucky | Benjamin Logan, a general and advocate for Kentucky's statehood in the Virginia legislature |
| Logan County | Ohio | Benjamin Logan, a general and advocate for Kentucky's statehood in the Virginia legislature |
| Logan County | West Virginia | Logan, a famous chief of the Mingo tribe |
| Long County | Georgia | Dr. Crawford W. Long, a pioneer anesthesiologist |
| Lonoke County | Arkansas | For a "lone oak" tree landmark |
| Lorain County | Ohio | The province of Lorraine, France |
| Los Alamos County | New Mexico | Los Alamos Ranch School, via Los Alamos National Laboratory, itself named for the Spanish los alamos, meaning "the cottonwoods" |
| Los Angeles County | California | Spanish for "the angels", originally Pueblo del Río de Nuestra Señora la Reina de Los Ángeles de Porciuncula ("Town of the River of Our Lady, Queen of the Angels") |
| Loudon County | Tennessee | Fort Loudoun, itself named for John Campbell, 4th Earl of Loudoun |
| Loudoun County | Virginia | John Campbell, 4th Earl of Loudoun, a commander of British forces during the French and Indian Wars |
| Louisa County | Iowa | Louisa Massey, an Iowa townswoman who avenged the murder of her brother |
| Louisa County | Virginia | Princess Louise of Great Britain, the youngest surviving daughter of George II of Great Britain |
| Loup County | Nebraska | The Loup River, from the French word for "wolf" |
| Love County | Oklahoma | Overton Love, a member of a Chickasaw family |
| Loving County | Texas | Oliver Loving, a cattle rancher and pioneer of the cattle drive |
| Lowndes County | Alabama | William Jones Lowndes, a lawyer and U.S. Congressman from South Carolina |
| Lowndes County | Georgia | William Jones Lowndes, a lawyer and U.S. Congressman from South Carolina |
| Lowndes County | Mississippi | William Jones Lowndes, a lawyer and U.S. Congressman from South Carolina |
| Lubbock County | Texas | Thomas Saltus Lubbock, a Texas Ranger and Confederate soldier during the American Civil War |
| Lucas County | Iowa | Robert Lucas, the first Governor of the Iowa Territory and the 12th Governor of Ohio |
| Lucas County | Ohio | Robert Lucas, the first Governor of the Iowa Territory and the 12th Governor of Ohio |
| Luce County | Michigan | Cyrus G. Luce, the 21st Governor of Michigan |
| Lumpkin County | Georgia | Wilson Lumpkin, a U.S. Congressman and the 35th Governor of Georgia |
| Luna County | New Mexico | Solomon Luna, a rancher and political figure |
| Lunenburg County | Virginia | The Duchy of Brunswick-Lüneburg, an historical polity in northwestern Germany |
| Luzerne County | Pennsylvania | Anne-César, Chevalier de la Luzerne, French minister to the United States during the American Revolutionary War |
| Lycoming County | Pennsylvania | Delaware Indian word meaning "sandy creek" or "gravelly creek" |
| Lyman County | South Dakota | W.P. Lyman, a legislator of the Dakota Territory |
| City of Lynchburg | Virginia | John Lynch, who founded the first European settlement at the site |
| Lynn County | Texas | William Lynn, a soldier believed to have died defending the Alamo |
| Lyon County | Iowa | Nathaniel Lyon, the first Union general killed in the American Civil War |
| Lyon County | Kansas | Nathaniel Lyon, the first Union general killed in the American Civil War |
| Lyon County | Kentucky | Nathaniel Lyon, the first Union general killed in the American Civil War |
| Lyon County | Minnesota | Nathaniel Lyon, the first Union general killed in the American Civil War |
| Lyon County | Nevada | Nathaniel Lyon, the first Union general killed in the American Civil War |

## M

| County name | State | Name origin |
| Mackinac County | Michigan | Named for the French interpretation of a Native American word meaning "great turtle", referring to the shape of nearby Mackinac Island as seen from a distance |
| Macomb County | Michigan | Alexander Macomb, a hero of the War of 1812 and later the Commanding General of the United States Army |
| Macon County | Alabama | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macon County | Georgia | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macon County | Illinois | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macon County | Missouri | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macon County | North Carolina | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macon County | Tennessee | Nathaniel Macon, a U.S. Congressman and President pro tempore of the U.S. Senate |
| Macoupin County | Illinois | Miami-Illinois term for the American lotus |
| Madera County | California | Spanish word for "wood", as lumbering was a major industry in the county at the time |
| Madison County | Alabama | James Madison, the 4th President of the United States |
| Madison County | Arkansas | James Madison, the 4th President of the United States |
| Madison County | Florida | James Madison, the 4th President of the United States |
| Madison County | Georgia | James Madison, the 4th President of the United States |
| Madison County | Idaho | James Madison, the 4th President of the United States |
| Madison County | Illinois | James Madison, the 4th President of the United States |
| Madison County | Indiana | James Madison, the 4th President of the United States |
| Madison County | Iowa | James Madison, the 4th President of the United States |
| Madison County | Kentucky | James Madison, the 4th President of the United States |
| Madison County | Mississippi | James Madison, the 4th President of the United States |
| Madison County | Missouri | James Madison, the 4th President of the United States |
| Madison County | New York | James Madison, the 4th President of the United States |
| Madison County | North Carolina | James Madison, the 4th President of the United States |
| Madison County | Ohio | James Madison, the 4th President of the United States |
| Madison County | Tennessee | James Madison, the 4th President of the United States |
| Madison County | Texas | James Madison, the 4th President of the United States |
| Madison County | Virginia | James Madison, the 4th President of the United States |
| Madison Parish | Louisiana | James Madison, the 4th President of the United States |
| Madison County | Montana | The Madison River, itself named for James Madison |
| Madison County | Nebraska | Madison, the capital of Wisconsin and the origin of most early settlers in the county, which was itself named for James Madison |
| Magoffin County | Kentucky | Beriah Magoffin, the 21st Governor of Kentucky |
| Mahaska County | Iowa | Chief Mahaska of the Iowa tribe |
| Mahnomen County | Minnesota | Ojibwe word for wild rice |
| Mahoning County | Ohio | Lenape word meaning "salt licks" |
| Major County | Oklahoma | John C. Major, a delegate to the Oklahoma Constitutional Convention |
| Malheur County | Oregon | The Malheur River which runs through it, itself named after the French word for "misfortune", referring to the unfortunate circumstance that some beaver furs cached near the river by early French Canadian voyageurs were stolen by local Indians |
| City of Manassas | Virginia | Manassas Junction, of uncertain origin; perhaps after a Jewish pedlar named Manasseh |
| City of Manassas Park | Virginia | Manassas Junction, of uncertain origin; perhaps after a Jewish pedlar named Manasseh |
| Manatee County | Florida | The West Indian manatee, an aquatic mammal native to the Florida coast |
| Manistee County | Michigan | The Manistee River, itself derived from a Native American word which means "river at whose mouth there are islands" |
| Manitowoc County | Wisconsin | Ojibwe manidoowaak, "spirit place" |
| Maʻopūtasi County | American Samoa | Samoan for "the only house of chiefs" |
| Marathon County | Wisconsin | Named for the Battle of Marathon, a famous battle of the Greco-Persian Wars in ancient Greece |
| Marengo County | Alabama | Named for the Battle of Marengo, fought in Italy during the Napoleonic-era War of the Second Coalition |
| Maricopa County | Arizona | The Maricopa people, a Native American tribe |
| Maries County | Missouri | Probably a corruption of the French word marais, meaning "marsh" |
| Marin County | California | Disputed; possibly named for Chief Marin of the Licatiut tribe or for the bay called Bahia de Nuestra Senora del Rosario la Marinera |
| Marinette County | Wisconsin | A corrupted form of Marie Antoinette, whose nickname "Marinette" was applied to Marguerite Chevalier, after whom the original town was actually named |
| Marion County | Alabama | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Arkansas | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Florida | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Georgia | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Illinois | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Indiana | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Iowa | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Kentucky | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Mississippi | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Missouri | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Ohio | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Oregon | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | South Carolina | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Tennessee | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Texas | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | West Virginia | Francis Marion, a Continental Army officer nicknamed the "Swamp Fox" for his activity in the Southern Theater of the American Revolutionary War |
| Marion County | Kansas | Named after Marion County, Ohio |
| Mariposa County | California | Spanish for "butterfly", as Spanish explorers encountered large clusters of butterflies where they named Mariposa Creek |
| Marlboro County | South Carolina | John Churchill, 1st Duke of Marlborough, an English soldier and statesman |
| Marquette County | Michigan | Père Jacques Marquette, a French Jesuit missionary and one of the first Europeans to explore and map the upper Mississippi River |
| Marquette County | Wisconsin | Père Jacques Marquette, a French Jesuit missionary and one of the first Europeans to explore and map the upper Mississippi River |
| Marshall County | Alabama | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Illinois | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Indiana | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Iowa | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Kentucky | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Mississippi | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Tennessee | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | West Virginia | John Marshall, the 4th Chief Justice of the Supreme Court and the 4th U.S. Secretary of State |
| Marshall County | Kansas | Francis J. Marshall, a military officer who established a ferry there and a member of the first state legislature |
| Marshall County | Minnesota | William Rainey Marshall, the 5th Governor of Minnesota |
| Marshall County | Oklahoma | The maiden name of the mother of George A. Henshaw, a delegate to the Oklahoma Constitutional Convention |
| Marshall County | South Dakota | Marshall Vincent, a county resident |
| Martin County | Florida | John W. Martin, the 24th Governor of Florida |
| Martin County | Indiana | John T. Martin of Kentucky |
| Martin County | Kentucky | John Preston Martin, a U.S. Congressman and state legislator |
| Martin County | Minnesota | Uncertain; either Henry Martin, a prominent landowner, or Morgan Lewis Martin, a U.S. Congressman from Wisconsin who introduced a bill for the organization of the Minnesota Territory |
| Martin County | North Carolina | Josiah Martin, the last colonial governor of North Carolina |
| Martin County | Texas | Wylie Martin, an early settler of the region |
| City of Martinsville | Virginia | Joseph Martin, a general in the Virginia militia during the American Revolutionary War and the city's founder |
| Mason County | Illinois | Named for Mason County, Kentucky |
| Mason County | Kentucky | George Mason, a Founding Father largely responsible for the Bill of Rights |
| Mason County | West Virginia | George Mason, a Founding Father largely responsible for the Bill of Rights |
| Mason County | Michigan | Stevens T. Mason, the first Governor of Michigan |
| Mason County | Texas | Fort Mason, itself named for George Thomson Mason, a U.S. Army lieutenant killed during the Mexican–American War |
| Mason County | Washington | C.H. Mason, the first secretary of the Washington Territory |
| Massac County | Illinois | Claude Louis d'Espinchal, marquis de Massiac, a French Naval Minister |
| Matagorda County | Texas | Spanish for "thick bush", after the canebrakes that once lined the Gulf of Mexico coastline |
| Matanuska-Susitna Borough | Alaska | Matanuska River and Susitna River |
| Mathews County | Virginia | Thomas Mathews, a state legislator |
| Maui County | Hawaii | Named after Maui, the largest and most populous of the five islands that make up the county |
| Maury County | Tennessee | Abram Poindexter Maury, Sr., a pioneer, farmer, and state senator |
| Maverick County | Texas | Samuel Augustus Maverick, a lawyer and rancher whose stubborn independence, allegedly for refusing to brand his cattle, is the origin of the word "maverick" |
| Mayes County | Oklahoma | Named for a prominent family and two chiefs of the Cherokee Nation |
| McClain County | Oklahoma | Charles M. McClain, a member of the Oklahoma Constitutional Convention |
| McCone County | Montana | George McCone, a state senator |
| McCook County | South Dakota | Edwin McCook, a Union Army officer during the American Civil War and Secretary of the Dakota Territory |
| McCormick County | South Carolina | Cyrus McCormick, a businessman often credited as the inventor of the mechanical reaper |
| McCracken County | Kentucky | Virgil McCracken, a hero of the War of 1812 |
| McCreary County | Kentucky | James B. McCreary, the 27th and 37th Governor of Kentucky |
| McCulloch County | Texas | Benjamin McCulloch, a Texas Ranger and Confederate general during the American Civil War |
| McCurtain County | Oklahoma | Named for three brothers who were each principal chiefs of the Choctaw Nation |
| McDonald County | Missouri | Alexander McDonald, a soldier during the American Revolutionary War |
| McDonough County | Illinois | Thomas Macdonough, a naval officer and hero of the War of 1812 who defeated the British on Lake Champlain during the Battle of Plattsburgh |
| McDowell County | North Carolina | Joseph McDowell Jr., an officer during the American Revolutionary War and later a U.S. Congressman |
| McDowell County | West Virginia | James McDowell, the 29th Governor of Virginia |
| McDuffie County | Georgia | George McDuffie, the 55th Governor of South Carolina |
| McHenry County | Illinois | William McHenry, a military officer in the War of 1812 and the Black Hawk War and a state legislator |
| McHenry County | North Dakota | James McHenry, an early settler |
| McIntosh County | Georgia | The McIntosh clan, which pioneered the area |
| McIntosh County | North Dakota | Edward H. McIntosh, a member of the state legislature |
| McIntosh County | Oklahoma | A prominent family of the Creek Nation |
| McKean County | Pennsylvania | Thomas McKean, the 2nd President of Delaware and the 2nd Governor of Pennsylvania |
| McKenzie County | North Dakota | Alexander McKenzie, a powerful political leader |
| McKinley County | New Mexico | President William McKinley |
| McLean County | Illinois | John McLean, first representative in Congress from Illinois and U.S. Senator |
| McLean County | Kentucky | Judge Alney McLean, an officer in the War of 1812 |
| McLean County | North Dakota | John A. McLean, a prominent citizen and the first mayor of Bismarck |
| McLennan County | Texas | Neil McLennan, an early settler |
| McLeod County | Minnesota | Martin McLeod, a pioneer fur trader and member of the council in the territorial legislature |
| McMinn County | Tennessee | Joseph McMinn, speaker of the state senate and governor of Tennessee |
| McMullen County | Texas | John McMullen, an Irish founder of a colony in Texas |
| McNairy County | Tennessee | John McNairy, a Constitutional Convention delegate and U.S. district judge for Tennessee |
| McPherson County | Kansas | Major-General James Birdseye McPherson, who was killed in the Civil War |
| McPherson County | Nebraska | Major-General James Birdseye McPherson, who was killed in the Civil War |
| McPherson County | South Dakota | Major-General James Birdseye McPherson, who was killed in the Civil War |
| Meade County | Kansas | Major-General George C. Meade |
| Meade County | South Dakota | Major-General George C. Meade |
| Meade County | Kentucky | Capt. James Meade, a hero of the War of 1812 |
| Meagher County | Montana | Thomas Francis Meagher, acting Governor of the Montana Territory |
| Mecklenburg County | North Carolina | The German state of Mecklenburg-Strelitz. Could also be named for Charlotte of Mecklenburg, queen consort of George III of Great Britain. |
| Mecklenburg County | Virginia | Charlotte of Mecklenburg |
| Mecosta County | Michigan | Potawatomi chief Mecosta |
| Medina County | Ohio | The county was named for the Arabian city of Medina, the former home of the Islamic faith's prophet Mohammed |
| Medina County | Texas | The Medina River, itself named after Pedro Medina, a Spanish engineer |
| Meeker County | Minnesota | Bradley B. Meeker, jurist and member of the territorial legislature |
| Meigs County | Ohio | Return J. Meigs Jr., the 4th Governor of Ohio and 8th Postmaster General |
| Meigs County | Tennessee | Return J. Meigs Sr., an officer in the Continental Army |
| Mellette County | South Dakota | Arthur C. Mellette, the first governor of South Dakota and the last governor of Dakota Territory. |
| Menard County | Illinois | Pierre Menard, the first Lieutenant Governor of Illinois |
| Menard County | Texas | Michel Branamour Menard, the founder of Galveston, Texas |
| Mendocino County | California | Attributive form of the Spanish surname Mendoza, for either Antonio de Mendoza, Viceroy of New Spain, or Lorenzo Suarez de Mendoza, another Viceroy, after Cape Mendocino |
| Menifee County | Kentucky | Richard Hickman Menefee, a U.S. Congressman |
| Menominee County | Michigan | The Menominee, who lived in the vicinity, "Menominee" means "rice men" or "rice gatherers" |
| Menominee County | Wisconsin | For the coterminous Menominee Indian Reservation |
| Merced County | California | Spanish for "mercy", from the Merced River, named by a traveler after a long dusty journey |
| Mercer County | Illinois | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | Kentucky | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | New Jersey | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | Ohio | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | Pennsylvania | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | West Virginia | Hugh Mercer, an officer in the Continental Army killed in the Battle of Princeton |
| Mercer County | Missouri | John F. Mercer, a Revolutionary War general |
| Mercer County | North Dakota | William Henry Harrison Mercer, an early rancher |
| Meriwether County | Georgia | General David Meriwether, who served in the Revolutionary War and was a state legislator and a member of congress |
| Merrick County | Nebraska | Elvira Merrick, wife of Henry W. DePuy, a territorial legislator |
| Merrimack County | New Hampshire | The Merrimack River, probably of Native American origin, but conjectural |
| Mesa County | Colorado | Named for Grand Mesa, a large flat-topped geologic formation near Grand Junction |
| Metcalfe County | Kentucky | Thomas Metcalfe, officer in the War of 1812, and Kentucky governor |
| Miami County | Indiana | The Miami people, a Native American tribe |
| Miami County | Kansas | The Miami people, a Native American tribe |
| Miami County | Ohio | The Miami people, a Native American tribe |
| Miami-Dade County | Florida | An amalgamation of: Miami, named after the Miami River, which in turn is believed to be derived from the Mayaimi, a Native American tribe that lived in South Florida until the 18th century Dade County, Florida, named after Major Francis L. Dade, a soldier killed in 1835 in the Second Seminole War |
| Middlesex County | Connecticut | Middlesex, one of the historic counties of England |
| Middlesex County | Massachusetts | Middlesex, one of the historic counties of England |
| Middlesex County | New Jersey | Middlesex, one of the historic counties of England |
| Middlesex County | Virginia | Middlesex, one of the historic counties of England |
| Midland County | Michigan | For its location near the geographical center of the Lower Peninsula |
| Midland County | Texas | For its location midway between Fort Worth and El Paso on the Texas and Pacific Railroad |
| Mifflin County | Pennsylvania | The first governor of Pennsylvania, Thomas Mifflin |
| Milam County | Texas | Benjamin Rush Milam, an early Texas colonizer and soldier killed in the Texas Revolution |
| Millard County | Utah | President Millard Fillmore |
| Mille Lacs County | Minnesota | French for "thousand lakes" |
| Miller County | Arkansas | James Miller, the first governor of the Arkansas Territory and a Brigadier General during the War of 1812. |
| Miller County | Georgia | Judge Andrew J. Miller, who served as a commander of the Oglethorpe Infantry |
| Miller County | Missouri | John Miller, governor of Missouri |
| Mills County | Iowa | named for Major Frederick Mills, killed in the Mexican–American War. |
| Mills County | Texas | John T. Mills, an early judge in Texas |
| Milwaukee County | Wisconsin | uncertain, but believed to be from a Potawatomi word "Mahnawaukee-Seepe" meaning "gathering place by the river." |
| Miner County | South Dakota | named for territorial legislators Nelson Miner and Ephriam Miner. |
| Mineral County | Colorado | Named for the economically valuable mineral resources found in the county |
| Mineral County | Montana | Named for the economically valuable mineral resources found in the county |
| Mineral County | Nevada | Named for the economically valuable mineral resources found in the county |
| Mineral County | West Virginia | Named for the economically valuable mineral resources found in the county |
| Mingo County | West Virginia | Named for the Mingo Indian tribe |
| Minidoka County | Idaho | Derived from a Dakota Sioux word meaning "a fountain or spring of water" |
| Minnehaha County | South Dakota | Derived from a Native American word meaning "river waterfall" |
| Missaukee County | Michigan | Named for Ottawa chief Missaukee |
| Mississippi County | Arkansas | The Mississippi River, itself named after the Ojibwe term for "great river" |
| Mississippi County | Missouri | The Mississippi River, itself named after the Ojibwe term for "great river" |
| Missoula County | Montana | A contraction of the Flathead word im-i-sul-e-etiku, meaning "near the place of fear" |
| Mitchell County | Georgia | Uncertain; either Henry Mitchell, a hero of the American Revolutionary War and president of the state senate, or David Brydie Mitchell, governor |
| Mitchell County | Iowa | Named by Irish settlers for John Mitchel (sic), an Irish nationalist who escaped to the U.S. |
| Mitchell County | Kansas | William D. Mitchell, a Union Army officer killed during the American Civil War |
| Mitchell County | North Carolina | Elisha Mitchell, an explorer of Mount Mitchell |
| Mitchell County | Texas | Asa and Eli Mitchell, early settlers of Stephen F. Austin's colony |
| Mobile County | Alabama | From the Muskhogean name for the town of Mauvila, found by the first explorers |
| Modoc County | California | The Modoc people, a Native American tribe |
| Moffat County | Colorado | David Moffat, a railroad tycoon and banker |
| Mohave County | Arizona | The Mohave people, a Native American tribe |
| Moniteau County | Missouri | French spelling of an Indian word meaning "spirit of God" |
| Monmouth County | New Jersey | Monmouthshire, a county in southeast Wales |
| Mono County | California | Mono Lake, itself named for an Indian tribe, possibly from monachie, meaning "fly people", referring to an insect that formed part of their diet |
| Monona County | Iowa | Disputed; possibly the name of a legendary bereaved Indian girl who leaped into the Mississippi River, or the name of an Indian divinity, or an Ottawa word meaning "beautiful land" |
| Monongalia County | West Virginia | Variant spelling of the Monongahela River, which means "unstable river banks" |
| Monroe County | Alabama | James Monroe, the 5th President of the United States |
| Monroe County | Arkansas | James Monroe, the 5th President of the United States |
| Monroe County | Florida | James Monroe, the 5th President of the United States |
| Monroe County | Georgia | James Monroe, the 5th President of the United States |
| Monroe County | Illinois | James Monroe, the 5th President of the United States |
| Monroe County | Indiana | James Monroe, the 5th President of the United States |
| Monroe County | Iowa | James Monroe, the 5th President of the United States |
| Monroe County | Kentucky | James Monroe, the 5th President of the United States |
| Monroe County | Michigan | James Monroe, the 5th President of the United States |
| Monroe County | Mississippi | James Monroe, the 5th President of the United States |
| Monroe County | Missouri | James Monroe, the 5th President of the United States |
| Monroe County | New York | James Monroe, the 5th President of the United States |
| Monroe County | Ohio | James Monroe, the 5th President of the United States |
| Monroe County | Pennsylvania | James Monroe, the 5th President of the United States |
| Monroe County | Tennessee | James Monroe, the 5th President of the United States |
| Monroe County | West Virginia | James Monroe, the 5th President of the United States |
| Monroe County | Wisconsin | James Monroe, the 5th President of the United States |
| Montague County | Texas | Daniel Montague, a state senator and early surveyor of the county |
| Montcalm County | Michigan | Louis-Joseph de Montcalm |
| Monterey County | California | The Spanish words monte and rey, together meaning "king of the forest"; Monterey Bay was named in honor of the Conde de Monterey, the Viceroy of New Spain |
| Montezuma County | Colorado | Moctezuma II, the last ruler of the Aztecs in central Mexico; the county's world-famous Mesa Verde ruins were once thought to have been built by the Aztecs |
| Montgomery County | Alabama | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Arkansas | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Georgia | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Illinois | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Indiana | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Iowa | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Kentucky | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Maryland | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Mississippi | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Missouri | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | New York | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | North Carolina | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Ohio | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Texas | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Virginia | Richard Montgomery, an officer during the American Revolutionary War |
| Montgomery County | Kansas | Uncertain; either James M. Montgomery, an abolitionist and preacher, or Richard Montgomery |
| Montgomery County | Pennsylvania | Uncertain; either Richard Montgomery or Montgomeryshire, a county in Wales, as that part of Pennsylvania was settled by Welsh Quakers |
| Montgomery County | Tennessee | John Montgomery, an explorer and Indian fighter |
| Montmorency County | Michigan | Raymond de Montmorency, a French officer who helped the colonies against England during the American Revolutionary War |
| Montour County | Pennsylvania | Madame Montour, a woman of Indian and French descent who was prominent in the Indian affairs |
| Montrose County | Colorado | The town of Montrose, which itself is named after the novel A Legend of Montrose by Sir Walter Scott |
| Moody County | South Dakota | Gideon C. Moody, a territorial legislator and later U.S. Senator |
| Moore County | North Carolina | Alfred Moore, an officer during the American Revolutionary War and a U.S. Supreme Court justice |
| Moore County | Tennessee | William Moore, an officer during the War of 1812 and later a state legislator |
| Moore County | Texas | Edwin Ward Moore, a Republic of Texas naval officer |
| Mora County | New Mexico | Uncertain; either from names of early settlers, such as Mora Pineda and Garcia de la Mora, or from the Spanish word meaning "blackberry" or "mulberry" |
| Morehouse Parish | Louisiana | Abraham Morehouse, an early settler |
| Morgan County | Alabama | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Georgia | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Illinois | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Indiana | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Kentucky | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Missouri | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Ohio | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Tennessee | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | West Virginia | Daniel Morgan, an officer during the American Revolutionary War and a U.S. representative |
| Morgan County | Colorado | The town of Fort Morgan (the county seat), itself named for U.S. Army Colonel Christopher A. Morgan, an aide to Civil War general John Pope |
| Morgan County | Utah | Jedediah Morgan Grant, a prominent Mormon churchman |
| Morrill County | Nebraska | Charles Henry Morrill, a regent of the University of Nebraska |
| Morris County | Kansas | Thomas Morris, a U.S. Senator |
| Morris County | New Jersey | Lewis Morris, a colonial governor of the Province of New Jersey |
| Morris County | Texas | W.W. Morris, a prominent attorney in east Texas |
| Morrison County | Minnesota | William and Allan Morrison, fur traders |
| Morrow County | Ohio | Jeremiah Morrow, the 9th Governor of Ohio |
| Morrow County | Oregon | Jackson L. Morrow, a member of the first state legislature |
| Morton County | Kansas | Oliver Hazard Perry Throck Morton, a jurist and U.S. Senator |
| Morton County | North Dakota | Oliver Hazard Perry Throck Morton, a jurist and U.S. Senator |
| Motley County | Texas | Junius William Mottley, a signer of the Texas Declaration of Independence |
| Moultrie County | Illinois | William Moultrie, an officer during the American Revolutionary War and the 35th Governor of South Carolina |
| Mountrail County | North Dakota | "Savage" Joseph Mountraille, a prominent voyageur who carried the mail |
| Mower County | Minnesota | John Mower, a territorial and state legislator |
| Muhlenberg County | Kentucky | Peter Muhlenberg, a clergyman and soldier during the American Revolutionary War |
| Multnomah County | Oregon | From the Multnomah village on Sauvie Island, itself named after nemathlonamaq, probably meaning "downriver" |
| Murray County | Georgia | Thomas W. Murray, a state legislator |
| Murray County | Minnesota | William Pitt Murray, a state legislator |
| Murray County | Oklahoma | William H. Murray, the 9th Governor of Oklahoma |
| Muscatine County | Iowa | The Mascouten tribe of the Potawatomi, a name possibly meaning "burning island" |
| Muscogee County | Georgia | Muscogee people |
| Muskegon County | Michigan | The Muskegon River, itself named for the Ojibwa/Chippewa word mashkig, meaning "swamp" or "marsh" |
| Muskingum County | Ohio | Derived from the Shawnee mshkikwam, "swampy ground"; the Muskingum River flows through the county |
| Muskogee County | Oklahoma | Muscogee (Creek) Nation |
| Musselshell County | Montana | Named for mussels found on the banks of the Musselshell River |