330,262 people (2024 Census estimate, −0.2% since 2020)
726 square miles of land · 455 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.
41 active community water systems list Boulder County in the area they serve, reporting 428,162 people served in all (a system that crosses county lines counts its whole population).
| BOULDER CITY OF surface water · local government · CO0107152 | 166,080 served |
| LONGMONT CITY OF surface water · local government · CO0107485 | 104,178 served |
| ERIE TOWN OF surface water · local government · CO0162255 | 47,444 served |
| LAFAYETTE CITY OF surface water · local government · CO0107473 | 28,700 served |
| LOUISVILLE CITY OF surface water · local government · CO0107487 | 20,975 served |
| LEFT HAND WD surface water · local government · CO0107471 | 20,280 served |
| SUPERIOR MD NO 1 surface water · local government · CO0107725 | 17,900 served |
| LONGS PEAK WD surface water · local government · CO0107486 | 3,200 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 323 people were held in Boulder County's jail, in Vera's latest figure (2025). In 2020 it was about 252.
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.
2 school districts have their office in Boulder County. School taxes are usually the largest part of a property tax bill.
Spent $508.2 million — $449.7 million to run schools, about $14,100 per student, plus $31.1 million on buildings and equipment. Money in: $358.1 million local (mostly property tax), $196.2 million state, $32.1 million federal. Long-term debt: $433.6 million.
Spent $549 million — $490.1 million to run schools, about $17,206 per student, plus $15.1 million on buildings and equipment. Money in: $464.1 million local (mostly property tax), $88.2 million state, $26.3 million federal. Long-term debt: $749.3 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 Moderate compared with other U.S. counties. FEMA estimates natural hazards cost Boulder County about $125.3 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Very High; social vulnerability: Very Low.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
321 bridges in Boulder County: 103 in good condition, 211 fair, and 7 poor (2.2%). “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 36 ML WBND over BOULDER CREEK · built 1952 | 18,000 vehicles a day |
| SH 7 ML WBND over BOULDER CREEK · built 1938 | 15,000 vehicles a day |
| 3rd Ave WB over GW RR · built 1974 | 9,116 vehicles a day |
| Rock Creek Pkwy over Community Ditch · built 2000 | 7,760 vehicles a day |
| South Bowen Street over Left Hand Creek · built 1965 | 1,835 vehicles a day |
| No. 30th Street over Four Mile Creek · built 1973 | 1,424 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $879.8 million of work in Boulder County in fiscal 2025, about $2,660 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 Boulder 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 Boulder County built: brayden.ozark@gmail.com.
More of Colorado: the state government and every county in Colorado.
Nearby counties: Gilpin County (18 mi) · Broomfield County (21 mi) · Clear Creek County (31 mi) · Denver County (36 mi) · Jefferson County (36 mi) · Grand County (38 mi).