Keystone is a town in Pennington County, South Dakota, home to about 336 people across 3.0 square miles. Its ZIP code is 57751.
Homes sold for a median of $509 per square foot in the three months ending August 2026, a buyer’s market.
Each card is that ZIP code’s whole market, including any part outside Keystone. Seller’s market: under 4 months of supply; buyer’s market: over 6. Methodology
We’re writing up Keystone’s story and what everyday life there is like, for people thinking about moving in.
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| Nearest major airport | Denver International Airport (DEN)286 miles away |
|---|---|
| Closer regional airport | Rapid City Regional Airport (RAP)20 miles away |
| Nearest city of 250,000+ | Denver, CO295 miles away |
| Nearest city of 1 million+ | Chicago, IL808 miles away |
Straight-line distances from the center of Keystone; driving is longer.
Source: Airports from OurAirports (scheduled passenger service); city centers and populations from the U.S. Census Bureau.
Source: Members of Congress from the congress-legislators project; districts from the Census Bureau’s relationship files; governor and mayor from Wikidata.
Keystone had 240 residents in the 2020 census, down 23% since 2000.
It’s the 188th largest of 440 towns in South Dakota by population.
Pennington County grew from 5,610 residents in 1900 to 109,222 in 2020.
Pennington County, 1900–2020
Source: U.S. Census Bureau decennial censuses (counties 1900–1990 from the Bureau’s historical county file).
Average highs peak around 79°F in summer, and winter lows average 18°F. About 24.3 inches of rain and melted snow fall in a typical year, with about 59 inches of snow.
Source: NOAA 1991–2020 climate normals, Mt Rushmore Nmem, SD weather station (3 miles away).
52,402 jobs at 4,137 businesses in Pennington County. The biggest industries by employees:
Source: U.S. Census Bureau County Business Patterns 2023 (private employers; jobs counted where people work).
Nearest hospitals
Source: Hospitals from CMS Hospital General Information (ratings are CMS overall star ratings); straight-line distances.
Libraries (1 nearby)
Museums (2 nearby)
Theaters and performance venues
Counts are within about 1.5 miles of the center of town.
Source: Map data © OpenStreetMap contributors (openstreetmap.org/copyright), as mapped by volunteers; it can miss places or include closed ones.
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Town boundaries don’t always match ZIP codes: a ZIP code can cross into neighboring towns, and a town can share a ZIP code with its neighbors. Facts describe the town itself; market figures describe whole ZIP codes.