Jefferson, SD

Jefferson is a Union County city founded in 1859, about 12 miles south of Sioux City and part of the Sioux City metropolitan area. The 2020 census counted 475 residents. French-Canadian settlers formed much of the early community; by 1867, roughly 25 French-Canadian families lived here. The town's location near the Big Sioux and Missouri river system connected it to farm country, river crossings, and the larger Sioux City market. Horseshoe Lake, an oxbow, sits among the nearest local waters.

Jefferson's hardest early chapter came during the smallpox epidemic of 1880–81, when the town was quarantined and more than 82 people died. That history sits alongside a more festive tradition: Jefferson Days, also called Days of '59, marks the founding with a parade, fireworks, a car show, sports, and a movie in the park. The annual celebration brings the city's French-Canadian beginnings into a current community calendar. Jefferson remains a small South Dakota city on the edge of Iowa's urban orbit, with river country, a 1859 town plan, and a summer festival tying the pieces together.