Voter file loaded July 20, 2026 · figures are from that file, held as a fixed record
Jefferson County, Idaho has 17,426 active registered voters — 79.8% Republican, 3.2% Democratic, and 15.9% with no party affiliation, as of July 2026.
Party registration
Most reliable-voting precincts
| # | Precinct | Active voters | Supervoters | Supervoter % |
|---|---|---|---|---|
| 1 | 021 | 494 | 267 | 54.05% |
| 2 | 004 | 829 | 446 | 53.8% |
| 3 | 009 | 864 | 434 | 50.23% |
| 4 | 006 | 922 | 433 | 46.96% |
| 5 | 018 | 797 | 366 | 45.92% |
| 6 | 007 | 915 | 408 | 44.59% |
| 7 | 019 | 1,215 | 527 | 43.37% |
| 8 | 017 | 1,029 | 445 | 43.25% |
| 9 | 002 | 1,130 | 481 | 42.57% |
| 10 | 008 | 456 | 193 | 42.32% |
Supervoters are active registered voters who cast a ballot in at least 3 of the last 4 November general elections (2018–2024). Percentages are precinct totals from the official state voter file — no individual voter information is shown. Precincts with fewer than 400 active voters are excluded.
How Jefferson County voted for president
Election results are public records.
Jefferson County at a glance.
Jefferson County had an estimated 34,854 residents in July 2024, the 12th most populous of Idaho's 44 counties, up 12.8% since the 2020 census. Of those, 23,963 are 18 or older, the voting-age population, and 12.9% are 65 or older. Its 17,426 active registered voters equal about 72.7% of that voting-age population.
It covers 1,094 square miles of land (32 people per square mile), and 75.8% of residents live outside any incorporated city or town. The largest cities and towns are Rigby (5,683), Menan (734), Ririe (part) (643), Roberts (583) and Lewisville (446). The American Community Survey (2020-2024) puts it at a median age of 32.8, a median household income of $86,679, 27.4% of adults 25 and older holding a bachelor's degree or higher and 83.0% of occupied homes owned by the people living in them.
In 2024, 15,819 votes were cast for president, about 66.0% of the voting-age population; the Democratic ticket took 12.0% and the Republican ticket 85.2%. The two-party margin moved from R+66.1 in 2008 to R+73.2 in 2024.
- Population (2024 estimate)
- 34,854
- Population (2020 census base)
- 30,891
- Voting-age population (18+)
- 23,963
- Active voters per 100 adults
- 72.7
- Residents 65 and older
- 12.9%
- People per square mile
- 32
- Living outside incorporated places
- 75.8%
- Land area
- 1,094 sq mi
- Median age
- 32.8
- Median household income
- $86,679
- Adults 25+ with a bachelor's degree
- 27.4%
- Owner-occupied homes
- 83.0%
Largest cities and towns
- Rigby 5,683
- Menan 734
- Ririe (part) 643
- Roberts 583
- Lewisville 446
Presidential vote, 2008–2024
| Year | Democratic | Republican | Margin | Votes cast |
|---|---|---|---|---|
| 2024 | 12.0% | 85.2% | R+73.2 | 15,819 |
| 2020 | 11.7% | 85.4% | R+73.7 | 14,173 |
| 2016 | 8.5% | 73.5% | R+65.0 | 11,471 |
| 2012 | 11.4% | 86.9% | R+75.5 | 11,381 |
| 2008 | 15.7% | 81.8% | R+66.1 | 10,441 |
Sources: U.S. Census Bureau Vintage 2024 population estimates and 2024 Gazetteer; American Community Survey 2020–2024 5-year estimates; certified county presidential returns. Growth, density and turnout are simple arithmetic on those figures.
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