| Official Name: | Lake Petersburg, Illinois |
| Settlement Type: | Census-designated place |
| Pushpin Map: | Illinois#USA |
| Pushpin Label: | Lake Petersburg |
| Subdivision Type: | Country |
| Subdivision Name: | United States |
| Subdivision Type1: | State |
| Subdivision Name1: | Illinois |
| Subdivision Type2: | County |
| Subdivision Name2: | Menard |
| Unit Pref: | Imperial |
| Area Footnotes: | [1] |
| Area Total Km2: | 5.39 |
| Area Land Km2: | 4.68 |
| Area Water Km2: | 0.71 |
| Area Total Sq Mi: | 2.08 |
| Area Land Sq Mi: | 1.81 |
| Area Water Sq Mi: | 0.28 |
| Population As Of: | 2020 |
| Population Footnotes: | [2] |
| Population Total: | 740 |
| Population Density Km2: | 158.15 |
| Population Density Sq Mi: | 409.52 |
| Timezone: | Central (CST) |
| Utc Offset: | -6 |
| Timezone Dst: | CDT |
| Utc Offset Dst: | -5 |
| Elevation Ft: | 581 |
| Coordinates: | 39.9831°N -89.865°W |
| Postal Code Type: | ZIP Code |
| Postal Code: | 62675 (Petersburg) |
| Area Code: | Area code 217 |
| Blank Name: | GNIS feature ID |
| Blank Info: | 2629866 |
Lake Petersburg is a census-designated place in Menard County, Illinois, United States. Its population was 740 as of the 2020 census.[2] 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 2miles to the north.
According to the U.S. Census Bureau, the Lake Petersburg CDP has a total area of 2.08sqmi, within which the reservoir occupies 0.28sqmi, or 13.2% of the community's area.[1]