South Dakota Highway 239 (SD 239) is a 7.312-mile-long (11.768 km) state highway located entirely within McPherson County, South Dakota.

Its northern terminus is at 106th Street in the small community of Long Lake.

Approximately 3–4 miles (4.8–6.4 km) later, SD 239 curves slightly east to bypass a small lake.

It then curves back to the west and straightens out to a due north course for the last 3 miles (4.8 km) before it terminates at 106th Stree on the south side of Long Lake.

SD 239 then becomes 350th Avenue after this terminus, which continues to the North Dakota state line.