Longest rivers in the United States:

Missouri: 2,540 miles 
Mississippi: 2,340 miles
Yukon: 1,980 miles
Rio Grande: 1,900 miles
St. Lawrence: 1,900 miles
Arkansas: 1,460 miles
Colorado: 1,450 miles
Atchafalaya: 1,420 miles
Ohio: 1,310 miles
Red: 1,290 miles
Brazos: 1,280 miles
Columbia: 1,240 miles
Snake: 1,040 miles

(Source: Statistical Abstract of the U.S., 1986)