Tecumseh, OK. Tecumseh is a city in Pottawatomie County, Oklahoma, United States. The population was 6,457 at the 2010 census. Tecumseh is located at 35°15′44″N 96°56′5″W / 35.26222°N 96.93472°W / 35.26222; -96.93472 (35.262346, -96.934830). According to the United States Census Bureau, the city has a total area of 15.3 square miles (39.5 km²), of which, 15.0 square miles (39.0 km²) of it is land and 0.2 square miles (0.6 km²) of it (1.57%) is water.