Rankin is a borough in Allegheny County, Pennsylvania, United States, 8 miles (13 km) south of Pittsburgh on the Monongahela River. Early in the 20th century, Rankin specialized in manufacturing steel and wire goods. In 1900, 3,775 people lived in Rankin; in 1910, 6,042 people lived in Rankin; and in 1940, 7,470 people lived in Rankin. The population was 2,315 at the 2000 census.
Rankin is located at 40°24′40″N 79°52′44″W / 40.41111°N 79.87889°W / 40.41111; -79.87889 (40.411069, -79.878884).
According to the United States Census Bureau, the borough has a total area of 0.5 square miles (1.3 km²), of which, 0.4 square miles (1.1 km²) of it is land and 0.1 square miles (0.2 km²) of it (12.00%) is water.