Menard County is a county in the U.S. state of Illinois. According to the 2020 United States Census, it had a population of 12,297. Its county seat is Petersburg. Menard County is part of the Springfield, Illinois, IL Metropolitan Statistical Area.

Petersburg is a city in and the county seat of Menard County, Illinois, United States, on the bluffs and part of the floodplain overlooking the Sangamon River. It is part of the Springfield, Illinois Metropolitan Statistical Area. The population was 2,258 at the 2020 census, nearly unchanged from 2010. Petersburg is located approximately 2 miles (3 km) north of New Salem, the original location where Abraham Lincoln first settled, as he started his career.