Title: List of longest rivers in the United States by state
Content: 1) Mississippi River – 2320 mi ; 2) Tennessee River – 652 mi ; 3) Pearl River – 444 mi ; 4) Big Black River – 330 mi ; 5) Hatchie River – 238 mi ; 6) Chickasawhay River – 210 mi ; 7) Tombigbee River – 200 mi ; 8) Yazoo River – 188 mi ; 9) Leaf River – 180 mi ; 10) Yalobusha River – 165 mi  The Pearl River is the longest river that is entirely within Mississippi. See also List of rivers of Mississippi.
Title: List of longest rivers in the United States by state
Content: 1) Saint Lawrence River – 744 mi ; 2) Susquehanna River – 464 mi ; 3) Allegheny River – 325 mi ; 4) Hudson River – 315 mi ; 5) Delaware River – 301 mi ; 6) Genesee River – 157 mi ; 7) Mohawk River – 149 mi ; 8) Raquette River – 146 mi ; 9) Oswegatchie River – 137 mi ; 10) Black River – 125 mi  The Hudson River is the longest river that is entirely within New York State. See also List of rivers of New York.
Title: List of longest rivers in the United States by state
Content: 1) Missouri River – 2340 mi ; 2) North Platte River – 716 mi ; 3) White River – 580 mi ; 4) Niobrara River – 568 mi ; 5) Republican River – 453 mi ; 6) South Platte River – 439 mi ; 7) Big Blue River – 359 mi ; 8) Platte River – 310 mi ; 9) Elkhorn River – 290 mi  The Platte River is the longest river that is entirely within Nebraska. See also List of rivers of Nebraska.
Title: List of longest rivers in the United States by state
Content: 1) Mississippi River – 2320 mi ; 2) Cumberland River – 688 mi ; 3) Tennessee River – 652 mi ; 4) Clinch River – 300 mi ; 5) Duck River – 284 mi ; 6) Hatchie River – 238 mi ; 7) French Broad River – 213 mi ; 8) Elk River – 195 mi ; 9) Hiwassee River – 147 mi ; 10) Caney Fork – 143 mi  The Duck River is the longest river that is entirely within Tennessee. See also List of rivers of Tennessee.
Title: List of longest rivers in the United States by state
Content: 1) Missouri River – 2340 mi ; 2) Mississippi River – 2320 mi ; 3) White River – 722 mi ; 4) Des Moines River – 525 mi ; 5) St. Francis River – 426 mi ; 6) Black River – 300 mi ; 7) Gasconade River – 280 mi ; 8) Osage River – 276 mi ; 9) Meramec River – 229 mi ; 10) Chariton River – 218 mi  The Gasconade River is the longest river that is entirely within Missouri. See also List of rivers of Missouri.
Title: List of longest rivers in the United States by state
Content: 1) Ohio River – 981 mi ; 2) Wabash River – 503 mi ; 3) Scioto River – 231 mi ; 4) Great Miami River – 160 mi ; 5) Maumee River – 137 mi ; 6) Sandusky River – 133 mi ; 7) Tuscarawas River – 130 mi ; 8) Raccoon Creek – 114 mi ; 9) Auglaize River – 113 mi ; 10) Mahoning River – 113 mi  The Scioto River is the longest river that is entirely within Ohio. See also List of rivers of Ohio.
Title: List of longest rivers in the United States by state
Content: 1) Mississippi River – 2320 mi ; 2) Arkansas River – 1469 mi ; 3) Red River – 1360 mi ; 4) White River – 722 mi ; 5) Ouachita River – 548 mi ; 6) St. Francis River – 426 mi ; 7) Bayou Bartholomew – 364 mi ; 8) Black River – 300 mi ; 9) Little River – 222 mi ; 10) Bayou Macon – 218 mi  See also List of rivers of Arkansas.
Title: List of longest rivers in the United States by state
Content: 1) Ohio River – 981 mi ; 2) Susquehanna River – 464 mi ; 3) Allegheny River – 325 mi ; 4) Delaware River – 301 mi ; 5) West Branch Susquehanna River – 243 mi ; 6) Genesee River – 157 mi ; 7) Schuylkill River – 135 mi ; 8) Youghiogheny River – 134 mi ; 9) Monongahela River – 130 mi ; 10) Raystown Branch Juniata River – 123 mi  The West Branch Susquehanna River is the longest river that is entirely within Pennsylvania. See also List of rivers of Pennsylvania.
Title: List of longest rivers in the United States by state
Content: 1) Colorado River – 1450 mi ; 2) Green River – 730 mi ; 3) Bear River – 491 mi ; 4) San Juan River – 383 mi ; 5) Sevier River – 383 mi</li> ; 6) Dolores River – 250 mi</li> ; 7) Blacks Fork – 175 mi ; 8) Virgin River – 162 mi ; 9) White River – 160 mi ; 10) Price River – 137 mi  The Sevier River is the longest river that is entirely within Utah. See also List of rivers of Utah.
Title: List of longest rivers in the United States by state
Content: 1) Chattahoochee River/Appalachicola River – 430 mi ; 2) St. Johns River – 310 mi ; 3) Suwannee River – 246 mi ; 4) Ochlockonee River – 206 mi ; 5) Alapaha River – 202 mi ; 6) Conecuh River – 198 mi ; 7) Pea River – 154 mi ; 8) Indian River – 153 mi ; 9) Choctawhatchee River – 141 mi ; 10) Withlacoochee River (central Florida) – 141 mi</li>  The St. Johns River is the longest river that is entirely within Florida. See also List of rivers of Florida.

Question: what is the longest river in the united states?
Answer: Missouri River.