Lake Petersburg, Illinois
Census-designated place
Lake Petersburg Show map of Illinois Lake Petersburg Show map of the United States
Coordinates: 39°58′59″N 89°51′54″W / 39.98306°N 89.86500°W / 39.98306; -89.86500[1]
Country	United States
State	Illinois
County	Menard
Area [2]
• Total	2.08 sq mi (5.39 km2)
• Land	1.81 sq mi (4.68 km2)
• Water	0.28 sq mi (0.71 km2)
Elevation [1]	581 ft (177 m)
Population  (2020)[3]
• Total	740
• Density	409.52/sq mi (158.15/km2)
Time zone	UTC-6 (Central (CST))
• Summer (DST)	UTC-5 (CDT)
ZIP Code	62675 (Petersburg)
Area code	Area code 217
GNIS feature ID	2629866[1]
Website	lakepetersburg.org

Lake Petersburg is a census-designated place in Menard County, Illinois, United States. Its population was 740 as of the 2020 census.^[3] The unincorporated community centers on a small reservoir, which is used extensively by residents for recreation.

Lake Petersburg is southwest of the center of Menard County, surrounding a reservoir of the same name, built in a valley that flows to the Sangamon River less than a mile to the east. Petersburg, the Menard county seat, is 2 miles (3 km) to the north.

According to the U.S. Census Bureau, the Lake Petersburg CDP has a total area of 2.08 square miles (5.39 km²), within which the reservoir occupies 0.28 square miles (0.73 km²), or 13.2% of the community's area.^[2]

• Community website