How many counties are there in the United States?

There are 3,141 counties and county equivalents in the 50 States and the District of Columbia. They are categorized as follows:

3,007 entities named "County"
16 Boroughs in Alaska
11 Census Areas in Alaska (for areas not organized into Boroughs by the State)
64 Parishes in Louisiana
42 Independent Cities (1 in Maryland, 1 in Missouri, 1 in Nevada, and the remainder in Virginia)
1 District - the Federal District or District of Columbia.

This does not include Commonwealths and territories with what are generally county equivalents, which are as follows:

Puerto Rico - 78 Municipios
U.S. Virgin Islands - 2 Districts
Guam - 19 Election Districts
Northern Mariana Islands - 17 Districts
American Samoa - 5 Districts