578,533 people (2024 Census estimate, −0.8% since 2020)
764 square miles of land · 757 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.
47 active community water systems list Jefferson County in the area they serve, reporting 555,599 people served in all (a system that crosses county lines counts its whole population).
| ARVADA CITY OF surface water · local government · CO0130001 | 171,610 served |
| CONSOLIDATED MUTUAL MAPLE GROVE surface water · local government · CO0130020 | 81,400 served |
| GREEN MOUNTAIN WSD buys surface water · local government · CO0130321 | 49,400 served |
| BANCROFT CLOVER WSD buys surface water · local government · CO0130133 | 44,000 served |
| GOLDEN CITY OF surface water · local government · CO0130040 | 38,288 served |
| BEAR CREEK WSD buys surface water · local government · CO0130138 | 30,000 served |
| WHEAT RIDGE WATER DISTRICT buys surface water · local government · CO0130842 | 20,000 served |
| EVERGREEN MD surface water · local government · CO0130030 | 15,750 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 813 people were held in Jefferson County's jail, in Vera's latest figure (2025). In 2020 it was about 676.
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.
1 school district has its office in Jefferson County. School taxes are usually the largest part of a property tax bill.
Spent $1.3 billion — $1.1 billion to run schools, about $14,483 per student, plus $153.4 million on buildings and equipment. Money in: $664.4 million local (mostly property tax), $482.2 million state, $85.2 million federal. Long-term debt: $779.8 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: Relatively High compared with other U.S. counties. FEMA estimates natural hazards cost Jefferson County about $231.4 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Relatively High; social vulnerability: Very Low.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
468 bridges in Jefferson County: 159 in good condition, 279 fair, and 30 poor (6.4%). “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.
| US 6 ML over SH 121 ML · built 1972 | 101,000 vehicles a day |
| I 70 ML WBND over SH 391 ML · built 1967 | 57,000 vehicles a day |
| I 70 ML EBND over SH 391 ML · built 1967 | 57,000 vehicles a day |
| I 70 WB RAMP over US 6 ML · built 1969 | 53,000 vehicles a day |
| I 70 ML WBND over WEST 20TH AVE · built 1968 | 45,500 vehicles a day |
| I 76 ML WBND over CLEAR CREEK · built 1984 | 38,000 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $317.5 million of work in Jefferson County in fiscal 2025, about $545 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.
General election: Tuesday, November 3, 2026. Ballots mailed to voters: 2026-10-02 to 2026-10-09. Drop boxes open: 2026-10-12. In-person voting at voter centers: 2026-10-19 to 2026-11-03. Last day to register and still get a ballot by mail: 2026-10-26. Last suggested day to mail your ballot back: 2026-10-26. Election Day: 2026-11-03. Last day to fix a signature problem: 2026-11-12.
Source: Colorado Secretary of State, Oct. 2, 2026 · Colorado Secretary of State, Sept. 23, 2026 · Colorado Secretary of State — Election Day FAQs
The budget, property tax rates, audits, local officials and offices for Jefferson 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 Jefferson County built: brayden.ozark@gmail.com.
More of Colorado: the state government and every county in Colorado.
Nearby counties: Denver County (23 mi) · Clear Creek County (24 mi) · Douglas County (24 mi) · Gilpin County (25 mi) · Broomfield County (28 mi) · Boulder County (36 mi).