Interstate 29 enters South Dakota at North Sioux City by crossing over the Big Sioux River. It runs northwest until its interchange with South Dakota Highway 50 near Vermillion, where it turns north. The highway alignment is due north until just before Sioux Falls. In the Sioux Falls area, I-29 serves the western part of Sioux Falls while I-229 spurs off and serves eastern Sioux Falls. In northwestern Sioux Falls, I-29 meets Interstate 90. After that, it continues north past Brookings. At the intersection with South Dakota Highway 28, I-29 turns northwest toward Watertown. After Watertown, the highway continues north into North Dakota.