Lake Springfield is a 3,965-acre (16.05 km2) reservoir on the southeast edge of the city of Springfield, Illinois. It is 560 ft (170 m) above sea level. The lake was formed by building Spaulding Dam across Sugar Creek, a tributary of the Sangamon River. It is the largest municipally-owned body of water in Illinois. The lake and the lands adjoining it are all owned by City Water, Light & Power, the municipal utility for the city of Springfield, which operates the Dallman Power Plant at the lake's north end. Multiple city parks border its shores.

Springfield is the capital city of the U.S. state of Illinois and the county seat of Sangamon County. The city's population was 114,394 at the 2020 census, which makes it the state's seventh most-populous city, the second largest outside of the Chicago metropolitan area, and the largest in central Illinois. Approximately 208,000 residents live in the Springfield metropolitan area.