Decatur is a city in Root and Washington townships, Adams County, Indiana, United States. The city, which serves as the county seat of Adams County, takes its name after the prominent war hero Stephen Decatur, Jr., one of the captains of the original 6 frigates of the US navy. When Indiana claimed official statehood in 1816, Decatur's name was as well known and revered as any star/celebrity today, thus when the town of Decatur was founded in 1836 it took its name in honor of the war hero. The population of Decatur was 9,405 at the 2010 census
Decatur is located at 40°49′46″N 84°55′45″W / 40.82944°N 84.92917°W / 40.82944; -84.92917 (40.829581, -84.929185).
According to the United States Census Bureau, the city has a total area of 4.9 square miles (12.8 km²), of which, 4.9 square miles (12.7 km²) of it is land and 0.20% is water.