17,402 people (2024 Census estimate, +3.2% since 2020)
461 square miles of land · 38 people per square mile
“Highest” and “lowest” are just order, not grades: a high rank for poverty or hazard losses means more of it. Each figure's source is in its section below.
9 active community water systems list Union County in the area they serve, reporting 23,997 people served in all (a system that crosses county lines counts its whole population).
| SOUTH LINCOLN RURAL WATER SYSTEM groundwater · private · SD4600870 | 5,250 served |
| CLAY RURAL WATER SYSTEM groundwater · private · SD4600626 | 4,780 served |
| DAKOTA DUNES CID buys groundwater · local government · SD4602093 | 3,700 served |
| NORTH SIOUX CITY groundwater · local government · SD4600226 | 3,042 served |
| BERESFORD buys groundwater · local government · SD4600386 | 2,359 served |
| ELK POINT groundwater · local government · SD4600116 | 2,124 served |
| CLAY RWS/SOUTH UNION groundwater · private · SD4602185 | 1,447 served |
| ALCESTER buys groundwater · local government · SD4600004 | 820 served |
Source: U.S. EPA Safe Drinking Water Information System (SDWIS), active community systems, . Look up any system's violations and test results with EPA's search using its ID.
About 35 people were held in Union County's jail, in Vera's latest figure (2019), or 342 per 100,000 residents ages 15–64. In 2014 it was about 27.
Source: Vera Institute of Justice, Incarceration Trends (built from federal Bureau of Justice Statistics jail surveys). Counties without their own jail, or that share one, may show no figure.
4 school districts have their office in Union County. School taxes are usually the largest part of a property tax bill.
Spent $16.6 million — $15.6 million to run schools, about $11,215 per student, plus $175,000 on buildings and equipment. Money in: $12.9 million local (mostly property tax), $4.8 million state, $1.2 million federal. Long-term debt: $25.6 million.
Spent $8.7 million — $8.4 million to run schools, about $11,812 per student, plus $316,000 on buildings and equipment. Money in: $5.3 million local (mostly property tax), $3.5 million state, $703,000 federal. Long-term debt: $1.7 million.
Spent $8.6 million — $7.9 million to run schools, about $11,520 per student, plus $643,000 on buildings and equipment. Money in: $4.9 million local (mostly property tax), $3 million state, $613,000 federal. Long-term debt: $10,000.
Spent $5.1 million — $4.4 million to run schools, about $12,568 per student, plus $348,000 on buildings and equipment. Money in: $3.5 million local (mostly property tax), $1.6 million state, $497,000 federal. Long-term debt: $8.5 million.
Source: U.S. Census Bureau, 2023 Annual Survey of School System Finances. Districts are listed by the county of their main office; some serve neighboring counties too.
Source: County Health Rankings & Roadmaps 2025 (University of Wisconsin Population Health Institute), which gathers federal data (CDC, Census, and others); measures cover different recent years. Blank lines aren't reported for small counties.
Overall risk: Very Low compared with other U.S. counties. FEMA estimates natural hazards cost Union County about $16.3 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Relatively Moderate; social vulnerability: Very Low.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
169 bridges in Union County: 51 in good condition, 77 fair, and 41 poor (24.3%). “Poor” means a main part — the deck, the beams, or the supports — is rated 4 or lower on the federal 0–9 scale. It doesn't mean unsafe to drive; unsafe bridges are closed.
| I029 N over 302 ST (FAS 6372) · built 1960 | 8,020 vehicles a day |
| 48480 CO HWY 13 over GREEN CK · built 1985 | 500 vehicles a day |
| 47400 302 ST. over WEST BRULE CK · built 1960 | 435 vehicles a day |
| 30330 RIVER ROAD over CK · built 1972 | 325 vehicles a day |
| 30999 477TH AVE over CK · built 1989 | 300 vehicles a day |
| 31490 477TH AVE over BR BRULE CK · built 1955 | 300 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $35 million of work in Union County in fiscal 2025, about $2,083 per resident — to the county, cities, schools, hospitals, nonprofits and others.
Source: USAspending.gov, grants by place of performance, fiscal 2025 (Oct. 2024 to Sept. 2025). Search it by county to see each award.
From Grants.gov: posted grants listing county governments as eligible, soonest deadline first; research-only and overseas programs left out; list updated 2026-10-13, refreshed weekly. 62 are open in all. Cities, towns, school districts and nonprofits have their own lists there.
Registration deadlines, early voting and polling places for South Dakota are on the federal site vote.gov, which links to the state's official election office.
The budget, property tax rates, audits, local officials and offices for Union County come from the county's own records, which we haven't gathered — not gathered, never hidden. See what a full county site looks like, or ask to have Union County built: brayden.ozark@gmail.com.
More of South Dakota: the state government and every county in South Dakota.
Nearby counties: Clay County (18 mi) · Plymouth County, IA (23 mi) · Dixon County, NE (26 mi) · Sioux County, IA (30 mi) · Dakota County, NE (31 mi) · Lincoln County (31 mi).