Yankton County is a county in South Dakota, United States, on the state’s southern edge where the Missouri River separates it from Nebraska. It had a population of 23,310 at the 2020 census and covers 532 square miles (1,380 km2) — 521 square miles (1,350 km2) of land and 11 square miles (28 km2) of water — centred near 43°01′N 97°23′W.
Yankton is the county seat, and its postal code is 57078. The county holds one city, five towns, and one community shared with a neighboring county. It sits in the Central time zone and carries FIPS code 46135.
Towns & Villages in Yankton County
Yankton dominates the county both as seat and largest employer base; the five smaller towns sit along the Missouri and James river bottoms to its north and west.
| Place | Type | Township | Pop. | ZIP |
|---|---|---|---|---|
| Yankton | City · seat | — | 15,411 | 57078 |
| Gayville | Town | Gayville | 382 | 57031 |
| Volin | Town | Volin | 158 | 57072 |
| Lesterville | Town | — | — | — |
| Mission Hill | Town | Mission Hill | — | — |
| Utica | Town | Utica | — | — |
| Irene | Town (partial) | — | — | — |
Townships
Yankton County retains nine organized civil townships, several sharing a name with the town at their center.
| Township | Pop. (2020) | Main settlements |
|---|---|---|
| Gayville | — | Gayville |
| Jamesville | — | Jamesville, Jamesville Colony |
| Marindahl | — | rural farmland, no incorporated place |
| Mayfield | — | Mayfield |
| Mission Hill | — | Mission Hill |
| Turkey Valley | — | rural farmland, no incorporated place |
| Utica | — | Utica |
| Volin | — | Volin |
| Walshtown | — | rural farmland, no incorporated place |
ZIP Codes
- 57078 — Yankton (also serves the surrounding rural county seat area)
- 57031 — Gayville
- 57072 — Volin
Lesterville, Mission Hill, Utica, and Irene are too small to carry their own confirmed ZIP in current postal records available to this profile; residents there use a neighboring town’s postal code.
Geography
The county sits on rolling hills cut by creeks draining toward the Missouri River, which forms its southern boundary with Nebraska. Lewis and Clark Lake, a reservoir behind Gavins Point Dam, occupies the county’s southwestern corner and is the region’s main recreational draw, alongside the Missouri National Recreational River corridor downstream of the dam.
Yankton County borders six neighbors: Turner County to the northeast, Clay County to the east, Cedar County, Nebraska, to the southeast, Knox County, Nebraska, to the southwest, Bon Homme County to the west, and Hutchinson County to the northwest.
Demographics
Yankton County counted 23,310 residents at the 2020 census, with a 2025 estimate of 23,635 — slow, steady growth centred on the county seat. Yankton itself holds 15,411 of that total; Gayville, at 382, is the next-largest incorporated place. The county is 88.3% White, 3.0% American Indian, 1.4% Black, and 0.6% Asian, with 5.3% identifying as Hispanic or Latino, and a median age of 42.3 years.
South Dakota’s statewide 2023 ACS median household income is $71,810; Yankton County’s own figure runs somewhat below that mark, reflecting an economy still anchored in agriculture and small manufacturing rather than the higher-wage Sioux Falls corridor to the northeast. Population density works out to roughly 45 people per square mile.
Economy & Local Life
Row-crop and livestock agriculture dominates the county outside Yankton itself, with corn, soybeans, and cattle the mainstays on the rolling upland ground. Yankton carries the county’s broader employment base: Avera Sacred Heart Hospital, Yankton School District, Human Services Center (a state psychiatric facility), and several food-processing and metal-fabrication plants along the river. Lewis and Clark Lake draws a summer tourism trade of campers and anglers that supports marinas, bait shops, and lakeside resorts each season.
The county’s biggest annual event is Yankton’s Riverboat Days, held each August along the Missouri River, celebrating the town’s steamboat-era history with a parade, carnival, and fireworks.
History
Yankton County was organized on April 10, 1862, one of the first counties created in Dakota Territory, and takes its name from the Yankton Sioux (Ihanktonwan), whose ancestral territory covered this stretch of the Missouri River valley. Yankton served as the capital of Dakota Territory from 1861 until the capital moved to Bismarck in 1883, giving the county an outsized early role in the region’s political history. The Gavins Point Dam, completed in 1957, later reshaped the county’s southwestern corner by creating Lewis and Clark Lake and stabilizing river flow for the Missouri National Recreational River downstream.
Getting There
U.S. Route 81 runs north–south through Yankton, connecting to Interstate 29 near Sioux Falls, while South Dakota Routes 46, 50, 52, 153, and 314 link the county’s smaller towns to the seat.
- Sioux Falls — 65 miles northeast
- Vermillion — 30 miles east
- Sioux City, Iowa — 55 miles southeast
- Norfolk, Nebraska — 60 miles south
Chan Gurney Municipal Airport in Yankton offers scheduled commercial air service on a regional carrier. South Dakota has no Amtrak service; the nearest station is in Omaha, Nebraska, roughly 90 miles to the southeast.
Frequently Asked Questions
What is the Yankton postcode?
57078.
What is the population of Yankton County?
23,310 at the 2020 census, with a 2025 estimate of 23,635.
What is the county seat of Yankton County?
Yankton is the county seat, and also the county’s largest city.
How big is Yankton County?
532 square miles (1,380 km2) total, of which 521 square miles (1,350 km2) is land.
What towns are in Yankton County besides Yankton?
Gayville, Lesterville, Mission Hill, Utica, and Volin, plus a share of Irene.
What lake is in Yankton County?
Lewis and Clark Lake, formed by Gavins Point Dam on the Missouri River, sits in the county’s southwestern corner.
Which counties border Yankton County?
Turner and Hutchinson to the north, Clay to the east, Bon Homme to the west, and Cedar and Knox counties in Nebraska across the Missouri River to the south.
More counties in this state: Towns and villages in South Dakota.