South Dakota Highway 204 (SD 204) is a short 2.131-mile-long (3.430 km) east-west state highway in central South Dakota.

It serves as a crossing of the Missouri River, running directly overtop of the Oahe Dam.

SD 204 begins in Stanley County at an intersection between SD 1806 and an access road, which leads to some of the dam's facilities as well as the Oahe Downstream Recreation Area, located at the base of the dam near one of the spillways.

SD 204 run due northeast directly across the dam for nearly 1.5 miles, offering views of the lake and the valley below as it crosses into Hughes County at the site of the original Missouri River basin, before having an intersection with an access road to the power house and pulling away from the dam.

The highway passes by the historic Oahe Chapel before coming to an end at an intersection with SD 1804 several miles north of Pierre.