Sedan Old City Lake is located on the western edge of the unique Chautauqua Hills region in southeast Kansas. The area around the lake is characterized by sandstone covered hills, the tops of which are covered with Blackjack Oak trees. The lake's drainage basin consists of 3,040 acres of similar topography, but also includes some grassland covered Osage Questas ecotone. This helps to maintain the average 33 inches of water transparency. The lake is located three miles north of Sedan, Kansas on highway 99, then one half mile east. Construction of the lake was completed in 1935 by the Works Progress Administration, Civilian Conservation Corps, and City of Sedan. Their craftsmanship is still evident in the native limestone inlaid dam, spillway, shelters, retaining walls, and entrances. The lake was constructed for the purposes of flood control, civic water supply, and recreation. Sedan no longer uses the lake as its water supply.

The 55 acre lake is surrounded by 600 acres of City owned and managed property and also contains another water supply lake, Sedan New City Lake, below. The Old City Lake has a paved boat ramp, group picnic shelter, outhouse, electrical camping hook-ups, and three community buildings including a dining hall and swimming pool which it leases to a church camp. A solar powered automatic fish feeder was added in 2001. The Sedan Police Department patrols the lake regularly and closes the gate at night. These efforts are evidenced by the cleanliness and beauty retained by limestone structures around the lake.