Petersburg is a city within Washington Township and the county seat of Pike County, in the U.S. state of Indiana. The population was 2,383 at the 2010 census.

Pike County is a county in the southwest portion of the U.S. state of Indiana. As of the 2020 United States census, the population was 12,250. The county seat is Petersburg. It contains the geographic point representing median center of US population in 2010.