# Geographic Areas Reference Manual/Chapter 4

Chapter 4
States and counties are the major legally defined political and administrative units of the United States. As such, they serve as the primary geographic units for which the Bureau of the Census reports data. The Census Bureau provides statistics for these entities in every decennial census of population and housing, in every census of agriculture and governments, and in all the economic censuses. It tabulates data for States and counties in postcensal estimates and sometimes in its various intercensal sample surveys and projections as well. In certain circumstances, it classifies entities as the statistical equivalents of States or of counties for data presentation purposes.
Because States, counties, and statistically equivalent entities are an integral part of many Census Bureau data presentations, they occupy a prominent position in the hierarchy of the basic geographic entities (see Figure 2-1 in Chapter 2). Therefore, a major responsibility of the Census Bureau is to maintain accurate maps and records of the boundaries and names of these entities, and to identify their populations and other data items correctly throughout the various phases of the census process. This chapter describes the framework of the States, counties, and statistically equivalent entities used by the Census Bureau, and explains their function as geographic units in the process of data collection, tabulation, and dissemination.
The United States comprises the 50 States and the District of Columbia. For data presentation purposes, the Census Bureau treats the District of Columbia as the statistical equivalent of a State. Depending upon Federal law and the scope of a particular census, sample survey, estimate, or projection, the Census Bureau may apply the same treatment to the territories under U.S. sovereignty or jurisdiction; for the 1990 decennial census, these included American Samoa, Guam, the Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands of the United States. For several other entities under U.S. jurisdiction, the Census Bureau publishes only decennial census population counts and area measurements; for the 1990 census, these were the ​Midway Islands; Wake Island; Johnston Atoll; Navassa, Baker, Howland and Jarvis Islands; Kingman Reef; and Palmyra Atoll. In recent decennial censuses, the Census Bureau also provided statistics as State equivalents for the Canal Zone and the Trust Territory of the Pacific Islands (see Chapter 7, “Puerto Rico and the Outlying Areas”). The designation Commonwealth is part of the official name of four States (Kentucky, Massachusetts, Pennsylvania, and Virginia), of Puerto Rico, and of the Northern Mariana Islands. In the interest of uniformity, the Census Bureau does not use the term for its data presentations.
For most States, counties are the primary administrative divisions. There are exceptions, however; Louisiana has parishes, while Alaska has boroughs for the organized portion of its territory. Because a large part of Alaska is not in any organized borough, the State and the Census Bureau cooperatively have subdivided the unorganized portion of Alaska into census areas for the purposes of presenting statistical data. Three States (Maryland, Missouri, and Nevada) each have one city that is governmentally independent of county organization; Virginia currently has 41 such cities. For both legal and statistical presentation purposes, these independent cities constitute primary administrative divisions of their States. Part of Yellowstone National Park in Montana is not within any county, therefore the Census Bureau treats it as the statistical equivalent of a county. The District of Columbia has no primary administrative divisions; the Census Bureau treats its entire area as the statistical equivalent of both a State and a county.
The various entities that the Census Bureau treats as the statistical equivalents of counties in Puerto Rico and the Outlying Areas (see Chapter 7 for details) are as follows:
* American Samoa—3 districts and 2 islands; the counties in American Samoa are treated as minor civil divisions
* Guam—the entire island
* The Northern Mariana Islands—4 municipalities
* Palau—16 States ​
* Puerto Rico—78 municipios
* The Virgin Islands of the United States—3 islands
The formation of States and counties has been an important theme in the political and social history of the United States as the Nation acquired new areas, settled them, and organized territorial, State, and local governments. The present State boundaries evolved as the Nation expanded westward; at the same time, counties developed and spread as units of local government and administration within the States and territories. There were more than 2,000 counties formed in the period from 1790 to 1900. The various censuses of the United States have recognized these governmental units since the earliest enumerations.
The system of individual States within a Federal union has its roots in the American colonial experience. By the time of the American Revolution, the identity and boundaries of the original 13 States had been evolving during 150 years of British colonization and settlement. Under British rule, the colonial legislatures gradually achieved various degrees of autonomy and self-government. The present Federal Union began in 1789 under the Constitution. The original 13 States joined the United States by their act of ratification. Article IV, Section 3, of the Constitution provides for the admission of additional States. Thereby, both the national and State governments share the power to admit additional States. In the future, as in the past, an area could achieve statehood only by an act of Congress that follows the broad guidelines of this Constitutional provision.
In the colonial period, census-taking was a familiar element of the American scene; the colonial authorities undertook 27 enumerations of the various colonies between 1624 and 1773. Article I, Section 2, of the Constitution calls for a population census as the basis for apportioning the seats in the Congress. The requirement for a census and, implicitly, the recognition of States in the geographic structure of the Census Bureau’s ​data tabulations, became part of the new Federal Government’s powers and duties.
The 1790 census, the first national enumeration of the United States, included the original 13 States as well as other areas that later would be formed into States. At that time, Virginia included what is now the State of West Virginia. The first national census reported separate counts for the districts of Kentucky, Maine, Vermont, and the area that is now Tennessee. The actual enumeration covered only the settled area, or about one-third of the new Nation’s land area. It excluded much of northern Maine, upstate New York, and western and central Pennsylvania. West of the Alleghenies, the 1790 enumeration covered only a few settlements in present-day Kentucky and Tennessee. It included only the eastern third of present-day Georgia, and none of Alabama and Mississippi. However, it did not encompass any of the Northwest Territory, because that area was not under the effective control of the U.S. Government or any of the States.
New States generally originated as part of the process of western expansion and settlement, with the exceptions of Maine (created from Massachusetts) and West Virginia (created from Virginia). Census coverage followed closely behind the addition of new territory; as the frontier moved west, successive decennial enumerations covered the newly settled areas.
Identifying the many boundary shifts and name changes of the territories is beyond the scope of this chapter, as is providing detailed comparisons between the areas enumerated for the first time and the areas of the present-day States. Nevertheless, it is worthwhile to mention briefly some of these developments as they relate to the first coverage of areas in a decennial census of the United States. The maps in Figure 4-1 show the boundaries of the States and territories recognized for the 1790, 1850, and 1870 decennial censuses; the last major rearrangements of territorial boundaries and names occurred in the 1850s and 1860s. Table 4-1 shows the first decennial census that included the geographic area of each State, together with the date when each State was admitted to the Union. By the time of ​the 1870 census, except for the boundary separating the Dakotas and the merger of the two territories that formed Oklahoma, the States and territorial boundaries of the conterminous United States were essentially fixed. For convenience, the list refers to the States in terms of their present area and boundaries; except for the original 13, usually that area still was a territory or part of a territory at the time of its first Federal census, sometimes with a different name.
In almost all cases, each State or part of a State (other than the original 13) appeared in at least one decennial enumeration before it achieved statehood. The exception is Texas, which was an independent republic before its admission to the Union in 1845 and first appeared in the 1850 census. The 1880 census marked the first enumeration of Alaska. The 1890 census added the Indian Territory and the Oklahoma Territory (combined in 1907 to form the State of Oklahoma), and also reported data for American Indian reservations in other States and territories. The geographic coverage of the 1900 census, which added Hawaii, encompassed the entire area of the present United States.
The county originated as an administrative unit in England; early settlers brought the concept with them to the colonies. Throughout the colonial period, counties evolved as units of local government or administration. However, their importance varied from region to region in response to different economic, social, and political conditions. Long before the Revolution, three distinct systems had developed:
* In much of New England, the compact pattern of settlement favored the town as the local governing body; the county, a geographic grouping of towns, tended to be a legal entity that existed for judicial rather than general governmental purposes.
* In the South, with its dispersed farms and plantations, the county became the most important unit of local administration; towns (or townships) generally did not develop as local, self-governing units in the New England tradition. ​Table 4-1. Chronology of First Decennial Census Coverage of Each State
| Year of Census | First Decennial Census Coverage | Year Admitted to Statehood |
| 1790 | The Original 13 States | 1787 to 1790 |
| 1790 | District of Columbia | |
| 1790 | Vermont | 1791 |
| 1790 | Kentucky | 1792 |
| 1790 | Tennessee | 1796 |
| 1790 | Maine | 1820 |
| 1790 | West Virginia | 1863 |
| 1800 | Ohio | 1803 |
| 1800 | Indiana | 1816 |
| 1800 | Mississippi | 1817 |
| 1800 | Alabama | 1819 |
| 1810 | Louisiana | 1812 |
| 1810 | Illinois | 1818 |
| 1810 | Missouri | 1821 |
| 1810 | Arkansas | 1836 |
| 1810 | Michigan | 1837 |
| 1820 | — | — |
| 1830 | Florida | 1845 |
| 1840 | Iowa | 1846 |
| 1840 | Wisconsin | 1846 |
| 1850 | Texas | 1845 |
| 1850 | California | 1850 |
| 1850 | Minnesota | 1858 |
| 1850 | Oregon | 1858 |
| 1850 | Washington | 1889 |
| 1850 | Utah | 1896 |
| 1850 | New Mexico | 1912 |
| 1860 | Kansas | 1861 |
| 1860 | Nevada | 1864 |
| 1860 | Nebraska | 1867 |
| 1860 | Colorado | 1876 |
| 1860 | North Dakota | 1889 |
| 1860 | South Dakota | 1889 |
| 1860 | Arizona | 1912 |
| 1870 | Montana | 1889 |
| 1870 | Idaho | 1890 |
| 1870 | Wyoming | 1890 |
| 1880 | Alaska | 1959 |
| 1890 | Oklahoma | 1907 |
| 1900 | Hawaii | 1959 |
The United States in 1790
The United States in 1850
The United States in 1870
Later boundaries are shown with dashed lines. ​
These three systems of local government continued beyond the colonial period and became embodied in State constitutions and legislative acts. The 1790 census reported data for 292 counties. As the Nation expanded westward, the county form of local government followed; thus, the nineteenth century was the most active period of county formation (see Table 4-2).
| Decennial Census | Number of Counties and Parishes |
| 1790 | 0,292 |
| 1850 | 1,621 |
| 1870 | 2,247 |
| 1900 | 2,713 |
| 1920 | 3,041 |
The totals do not include statistical equivalents of counties (such as the independent cities of St. Louis and Baltimore and the cities of Virginia, some of which were independent as early as 1850).
The Northwest Ordinance provided for the establishment of local government in the newly settled territories, which later would become States. It empowered the territorial governors to create geographic divisions, which subsequently could serve as constituent units for representation in the territorial assembly. Legislators in the territories and new States usually laid out counties for the entire area of the jurisdiction. As a result, when new States gained admission to the Union, they often already had counties, although the less-settled portions of the State might have only a few very large counties, which would subsequently be subdivided as settlement expanded.
The process of county formation continued actively into the first two decades of the twentieth century. The largest single increase occurred in 1907 ​when Oklahoma became a State and organized 54 new counties from the Indian Territory. There were other sizable increases in county formation between 1910 and 1920, when Montana and Idaho almost doubled their number of existing counties by adding 23 and 21 new counties, respectively.
Since 1920, there have been relatively few new counties formed; in fact, only 12 States have formed new counties since then. Although Florida added 13 counties in the 1920s, few other States created more than 1 or 2 per decade; some States even lost counties as a result of mergers. Table 4-3 shows the number of counties and statistically equivalent entities at the time of the 1920 census and at the times of the six decennial censuses from 1940 through 1990. Most of the change in the number of statistically equivalent entities represents an increase in the number of independent cities in Virginia (from 20 at the time of the 1920 census to 41 for the 1980 and 1990 censuses) and the recognition of a variety of new entities statistically equivalent to counties in Alaska beginning with the 1960 census.
| Census Year | Counties/Statistical Equivalents | Counties/Parishes | Independent Cities and Other Statistically Equivalent Entities |
| 1920 | 3,064 | 3,041 | 23 |
| 1940 | 3,100 | 3,070 | 30 |
| 1950 | 3,103 | 3,070 | 33 |
| 1960 | 3,134 | 3,072 | 62 |
| 1970 | 3,141 | 3,069 | 72 |
| 1980 | 3,137 | 3,068 | 69 |
| 1990 | 3,141 | 3,070 | 71 |
* ↑ The independent cities include Baltimore city, St. Louis city, Carson City (as of 1970), and the cities of Virginia.
* ↑ Other statistically equivalent entities include the District of Columbia, the Alaska statistical areas, and that portion of Yellowstone National Park in Montana as of 1940. The entities statistically equivalent to counties in Alaska were known as election districts in 1960, census divisions in 1970, and boroughs/census areas in 1980 and 1990.
States and the statistically equivalent entities for which the Census Bureau tabulates data are legal entities, with boundaries prescribed by laws, treaties, and other governmental actions. Title 13, United States Code, in Chapter 5, “Censuses,” Subchapter II, sections 141(a) and (b), mandates the counting and tabulating of the population of the individual States and entities. Therefore, the Census Bureau uses the States, the District of Columbia, and the territories of the United States as a primary level of geography; it retains their identity throughout the data collection, tabulation, and dissemination phases of every census.
| Alabama | 67 |
| Alaska | 25 |
| Arizona | 15 |
| Arkansas | 75 |
| California | 58 |
| Colorado | 63 |
| Connecticut | 8 |
| Delaware | 3 |
| District of Columbia | 1 |
| Florida | 67 |
| Georgia | 159 |
| Hawaii | 5 |
| Idaho | 44 |
| Illinois | 102 |
| Indiana | 92 |
| Iowa | 99 |
| Kansas | 105 |
| Kentucky | 120 |
| Louisiana | 64 |
| Maine | 16 |
| Maryland | 24 |
| Massachusetts | 14 |
| Michigan | 83 |
| Minnesota | 87 |
| Mississippi | 82 |
| Missouri | 115 |
| Montana | 57 |
| Nebraska | 93 |
| Nevada | 17 |
| New Hampshire | 10 |
| New Jersey | 21 |
| New Mexico | 33 |
| New York | 62 |
| North Carolina | 100 |
| North Dakota | 53 |
| Ohio | 88 |
| Oklahoma | 77 |
| Oregon | 36 |
| Pennsylvania | 67 |
| Rhode Island | 5 |
| South Carolina | 46 |
| South Dakota | 66 |
| Tennessee | 95 |
| Texas | 254 |
| Utah | 29 |
| Vermont | 14 |
| Virginia | 136 |
| Washington | 39 |
| West Virginia | 55 |
| Wisconsin | 72 |
| Wyoming | 23 |
United States Total: 3,141
The United States total includes 3,006 counties; 14 boroughs and 11 census areas in Alaska; the District of Columbia; 64 parishes in Louisiana; Baltimore city, Maryland; St. Louis city, Missouri; that part of Yellowstone National Park in Montana; Carson City, Nevada; and 41 independent cities in Virginia.
Rhode Island’s counties exist only for the purpose of judicial administration and have no associated governmental structure. In 1960, Connecticut abolished its county governments and transferred their functions to the State government; however, the State retained the former counties for election and judicial purposes. Nevertheless, in both States, the Census Bureau continues to report many types of data for these county-type entities, in part to retain data comparability with earlier censuses and the data sets of other government agencies.
For Puerto Rico and the Outlying Areas, the Census Bureau uses various geographic units as the statistical equivalent of stateside counties. This occurs where the size, geography, or administrative framework make the units appropriate entities for such use. As in the 50 States, the statistical equivalents of counties in the Outlying Areas provide complete geographic coverage for the entire area and population of each jurisdiction (see Chapter 7).
To effectively collect, process, and tabulate data for States, counties, and their statistically equivalent entities, the Census Bureau must ensure that it has accurate records of the boundaries of, and names for, these entities. The Census Bureau also must develop appropriate geographic ​code schemes and geographic relationship files to properly control and present the data it collects for these important governmental units.
The boundaries of the primary governmental divisions of the United States, States, counties, and their statistical equivalents, generally are static and change only rarely; however, transfers of territory do occur from time to time. By contrast, the boundaries of incorporated places and even minor civil divisions are far more subject to change in most States.
Changes in State lines may result from legislation, court decisions, and other types of governmental action; changes in county boundaries are a matter of State law. Such boundary changes also may stem from more exact geographic descriptions, better maps, and improved surveying techniques. State boundaries may change by mutual agreement of the two State legislatures, subject to approval by the Congress.
In recent years, most boundary changes for counties have been minor and have not involved substantial shifts of population or land area. The independent cities in Virginia constitute an exception because they occasionally annex territory, as do the incorporated places in many States. Because the territory annexed by a Virginia city no longer is part of the county in which it had been located, changes in the boundaries of these independent cities also affect the boundaries of the adjacent county or counties. In other States, changes to counties occur on a piecemeal basis.
The Census Bureau has established procedures and programs to identify changes in legal boundaries and to record when and where they occur. The Census Bureau’s Boundary and Annexation Survey (BAS), conducted at periodic intervals immediately before each decennial census, and annually since 1972, determines the location of the boundaries of most major legal entities in the United States. The principal function of the BAS is to collect and maintain information on the inventory, status, boundaries, ​and names of local governments (counties, minor civil divisions, and incorporated places), and to ascertain whether changes have occurred in these entities. The Census Bureau obtains information about counties by sending questionnaires and maps to an official of each county (parish in Louisiana) in the United States, excluding Alaska, Connecticut, Hawaii, and Rhode Island; in these States, because of the unusual status of the counties (boroughs in Alaska), the Census Bureau works with the appropriate State authorities to obtain the required information. However, new counties (and boroughs in Alaska) are such a rare and major event that they usually come to the Census Bureau’s attention long before, and separate from, the annual BAS mailout. The Census Bureau obtains official confirmation and documentation of new counties, their boundaries, and their names from appropriate State officials.
Any changes in county boundaries may reflect changes in State boundaries as well. The proper location of State and county boundaries on Census Bureau maps is a vital element of the data collection and tabulation process. The BAS enables the Census Bureau to maintain, on a consistent basis, reasonably current records about changes in county boundaries that occur through resurveying, legal actions, or other transfers of territory that relocate county lines. In this way, the Census Bureau also accounts for changes in State lines as reported by the counties on either side of the State boundary.
The Census Bureau uses a system of numeric codes to identify every geographic entity in its hierarchy. These geographic codes are basic components of the geographic reference files that the Census Bureau develops and maintains to process the results of its censuses and sample surveys. The codes obviate the need to relate data to the geographic entities by name; that is, the Census Bureau’s processing operations associate data with the much shorter, fixed-length, unique numeric codes rather than the variable-length names of the geographic entities in its reference files. These files provide the basis for the tabulation and dissemination of the collected data in their proper geographic units.
​The Federal Government uses a unique two-digit numeric code to identify each State and State equivalent entity. These State codes are part of the Federal Information Processing Standards (FIPS), an official coding system developed by the National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards), U.S. Department of Commerce, and maintained by the U.S. Geological Survey (USGS). These FIPS codes parallel the alphabetic sequence of State names, including the District of Columbia, followed by Puerto Rico and the Outlying Areas in alphabetical order (see Table 4-5). Gaps left in the State numbering sequence provide for the possibility that a major Outlying Area may attain statehood using its current name. In addition, the FIPS for States includes a two-letter alphabetic code, used by both the NIST and the U.S. Postal Service, which has been adopted by many other Federal agencies.
In addition to the FIPS codes for States, the Census Bureau devised and uses a system of two-digit codes to identify each State in a geographic sequence within its census division. Each of the nine census divisions encompasses a group of adjacent States; the first digit of the Census Bureau’s State code identifies the division and the second digit refers to the geographic sequence of the individual State within that division. The territories under U.S. jurisdiction are not assigned to any of the nine census divisions, and their codes have a first digit of 0 in the Census Bureau’s scheme (see Table 4-5). Chapter 6, “Statistical Groupings of States and Counties,” presents a discussion of the census regions and divisions.
Another FIPS coding scheme that the Census Bureau uses identifies the counties alphabetically within each State. The FIPS 6 publication assigns each county a three-digit numeric code, with gaps in the numbering sequence to allow for additions and revisions. The independent cities appear at the end of the county list for each appropriate State, beginning with code 510.
​Table 4-5. Federal Abbreviations and Numeric Identification Codes for States, Outlying Areas, and Other Entities
| State/Statistically Equivalent Entity | FIPS/USPS Abbreviation | FIPS Code | Census Code |
| Alabama | AL | 01 | 63 |
| Alaska | AK | 02 | 94 |
| Arizona | AZ | 04 | 86 |
| Arkansas | AR | 05 | 71 |
| California | CA | 06 | 93 |
| Colorado | CO | 08 | 84 |
| Connecticut | CT | 09 | 16 |
| Delaware | DE | 10 | 51 |
| District of Columbia | DC | 11 | 53 |
| Florida | FL | 12 | 59 |
| Georgia | GA | 13 | 58 |
| Hawaii | HI | 15 | 95 |
| Idaho | ID | 16 | 82 |
| Illinois | IL | 17 | 33 |
| Indiana | IN | 18 | 32 |
| Iowa | IA | 19 | 42 |
| Kansas | KS | 20 | 47 |
| Kentucky | KY | 21 | 61 |
| Louisiana | LA | 22 | 72 |
| Maine | ME | 23 | 11 |
| Maryland | MD | 24 | 52 |
| Massachusetts | MA | 25 | 14 |
| Michigan | MI | 26 | 34 |
| Minnesota | MN | 27 | 41 |
| Mississippi | MS | 28 | 64 |
| Missouri | MO | 29 | 43 |
| Montana | MT | 30 | 81 |
| Nebraska | NE | 31 | 46 |
| Nevada | NV | 32 | 88 |
| New Hampshire | NH | 33 | 12 |
| New Jersey | NJ | 34 | 22 |
| New Mexico | NM | 35 | 85 |
| New York | NY | 36 | 21 |
| North Carolina | NC | 37 | 56 |
| North Dakota | ND | 38 | 44 |
| Ohio | OH | 39 | 31 |
| Oklahoma | OK | 40 | 73 |
| Oregon | OR | 41 | 92 ​ |
| Pennsylvania | PA | 42 | 23 |
| Rhode Island | RI | 44 | 15 |
| South Carolina | SC | 45 | 57 |
| South Dakota | SD | 46 | 45 |
| Tennessee | TN | 47 | 62 |
| Texas | TX | 48 | 74 |
| Utah | UT | 49 | 87 |
| Vermont | VT | 50 | 13 |
| Virginia | VA | 51 | 54 |
| Washington | WA | 53 | 91 |
| West Virginia | WV | 54 | 55 |
| Wisconsin | WI | 55 | 35 |
| Wyoming | WY | 56 | 83 |
| American Samoa | AS | 60 | 03 |
| Guam | GU | 66 | 04 |
| Northern Mariana Islands | MP | 69 | 01 |
| Palau | PW | 70 | 02 |
| Puerto Rico | PR | 72 | 06 |
| U.S. Virgin Islands | VI | 78 | 07 |
| Foreign Areas and International Waters | _ | 99 | _ |
| U.S. Minor Outlying Islands | OM | 74 | 08 |
| Baker Island | _ | 81 | 08 |
| Howland Island | _ | 84 | 08 |
| Jarvis Island | _ | 86 | 08 |
| Johnston Atoll | _ | 67 | 08 |
| Kingman Reef | _ | 89 | 08 |
| Midway Islands | _ | 71 | 08 |
| Navassa Island | _ | 76 | 08 |
| Palmyra Atoll | _ | 95 | 08 |
| Wake Island | _ | 79 | 08 |
* ↑ Foreign Areas and International Waters are areas bordering the United States and the Outlying Areas. They have no official NIST/USPS abbreviation and require no State-level code.
* ↑ The individual islands of the U.S. Minor Outlying Islands have no official NIST/USPS abbreviation.
Both States and counties provide complete coverage of all land area and population in the United States at their geographic levels. Almost all other geographic entities included in the Census Bureau’s data tabulations respect the boundaries of States. American Indian reservations, however, may cross State boundaries. Also, some U.S. Postal Service five-digit ZIP Codes extend into a second State. By design, statistical areas respect State lines, with two exceptions: both metropolitan areas (defined by the Office of Management and Budget) and urbanized areas may cross State boundaries.
Two types of statistical entities, the census region and the census division, encompass combinations of adjacent States. Both regions and divisions are convenient geographic units for summarizing census and sample survey data. For instance, the six New England States compose a single division; together with the Middle Atlantic Division, they form the Northeast Region (see Chapter 6, “Statistical Groupings of States and Counties”).
The nationwide geographic framework provided by the county makes it possible to combine counties and statistically equivalent entities into larger statistical units, which may encompass an entire State or selected parts of several States. One of the best known examples of county combinations are metropolitan areas (see Chapter 13, “Metropolitan Areas”).
At lower levels of the geographic hierarchy, most geographic areas respect the boundaries of counties and county equivalents. The county subdivisions, census county divisions, minor civil divisions, and unorganized territories, provide complete coverage of all land area and population within each county and statistically equivalent entity. On the other hand, in most States, incorporated places may cross county lines; census designated places may do so in all States. Some incorporated places, such as Philadelphia and San Francisco, comprise the entire area of a county (the city of New York encompasses five entire counties); for such entities, the city and county usually have a single government. In five instances at the time of the 1990 ​census, a county and city consolidated their governments, and yet other incorporated places continued to function within the county; the Census Bureau treats these entities as both counties and consolidated cities (see Chapter 9, “Places”). The small-area components of decennial census geography, census tracts/block numbering areas and their subdivisions (block groups and census blocks, and enumeration districts prior to the 1990 census), always observe county boundaries.