Lake Springfield is a 3,965-acre reservoir in the southeast of the capital city of Springfield, Illinois. It is 560 ft 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 Wate…Lake Springfield is a 3,965-acre reservoir in the southeast of the capital city of Springfield, Illinois. It is 560 ft 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 more than 50 miles of shoreline.