Idaho counties by area
Official, comparable measurements for 44 counties and county equivalents.
- 406.9–729.3 mi²
- 757.2–1,112.5 mi²
- 1,199–1,763.1 mi²
- 1,764.2–2,565.6 mi²
- 2,637.5–8,477.5 mi²
- 0.44–3.7 per mi²
- 3.7–7.6 per mi²
- 7.7–24 per mi²
- 24–51 per mi²
- 51–519 per mi²
Understanding Idaho’s county areas
The land-area range runs from Payette County at 406.9 mi² to Idaho County at 8,477.5 mi². The largest has 20.8 times the land area of the smallest and accounts for 10.3% of the combined county land in Idaho. Compare with every state’s largest county.
The median county-equivalent land area is 1,315.7 mi², above the national median of 604.5 mi². The median describes the middle of the county size distribution; it does not describe how people or development are distributed. A state with a few very large counties can have a much smaller median than its largest entry suggests.
Where water changes the picture
Bonner County has the most assigned water area, at 184.9 mi². It also has the highest water share, with water making up 9.6% of its total area. Water area and water percentage answer different questions: the first measures an amount, while the second measures the mix of land and water.
Across all 44 entries, water accounts for 1.1% of the combined total area. This is calculated from the summed land and water measurements, rather than averaging county percentages, which would give each small and large county equal weight.
Where people live
An estimated 2,029,733 people lived in Idaho on July 1, 2025 (+10.4% since 2020), or 0.6% of the national total in this dataset. Ada County is the most populous county equivalent, with 546,141 residents — 26.9% of the state. The largest by land, Idaho County, has 17,874.
Across the state there are 25 people per square mile of land. County densities range from 519 in Ada County to 0.44 in Clark County; the median county equivalent has 10. Switch the map above to density to see where the state’s population concentrates.
Compare the largest and smallest county equivalents in Idaho to see land, water, and total area on the same scale.
These calculations use the 2026 Census county records listed below. County-equivalent boundaries vary between states; area alone does not measure population, density, or usable land. See coverage and calculation rules.
Complete area table
Sorted from largest to smallest land area.
| # | County / equivalent | Land | Water | Water share | Population | Per mi² |
|---|---|---|---|---|---|---|
| 1 | Idaho CountyGEOID 16049 | 8,477.5 mi² | 26.1 mi² | 0.3% | 17,874 | 2.1 |
| 2 | Owyhee CountyGEOID 16073 | 7,668.2 mi² | 28.6 mi² | 0.4% | 12,661 | 1.7 |
| 3 | Custer CountyGEOID 16037 | 4,922.2 mi² | 16.4 mi² | 0.3% | 4,636 | 0.94 |
| 4 | Lemhi CountyGEOID 16059 | 4,563.7 mi² | 5.4 mi² | 0.1% | 8,474 | 1.9 |
| 5 | Valley CountyGEOID 16085 | 3,665.1 mi² | 68.4 mi² | 1.8% | 12,831 | 3.5 |
| 6 | Elmore CountyGEOID 16039 | 3,075.1 mi² | 26.4 mi² | 0.9% | 29,465 | 9.6 |
| 7 | Blaine CountyGEOID 16013 | 2,637.7 mi² | 17.2 mi² | 0.6% | 25,517 | 9.7 |
| 8 | Shoshone CountyGEOID 16079 | 2,637.5 mi² | 5.4 mi² | 0.2% | 14,130 | 5.4 |
| 9 | Cassia CountyGEOID 16031 | 2,565.6 mi² | 15.1 mi² | 0.6% | 26,397 | 10 |
| 10 | Clearwater CountyGEOID 16035 | 2,453.4 mi² | 30.7 mi² | 1.2% | 9,118 | 3.7 |
| 11 | Butte CountyGEOID 16023 | 2,236.5 mi² | 2 mi² | 0.1% | 2,783 | 1.2 |
| 12 | Bingham CountyGEOID 16011 | 2,093.7 mi² | 26.5 mi² | 1.2% | 51,153 | 24 |
| 13 | Twin Falls CountyGEOID 16083 | 1,921.7 mi² | 7 mi² | 0.4% | 97,539 | 51 |
| 14 | Boise CountyGEOID 16015 | 1,899.4 mi² | 7.4 mi² | 0.4% | 8,545 | 4.5 |
| 15 | Bonneville CountyGEOID 16019 | 1,866 mi² | 34.3 mi² | 1.8% | 135,771 | 73 |
| 16 | Fremont CountyGEOID 16043 | 1,864 mi² | 32.2 mi² | 1.7% | 14,208 | 7.6 |
| 17 | Caribou CountyGEOID 16029 | 1,764.2 mi² | 34.4 mi² | 1.9% | 7,252 | 4.1 |
| 18 | Clark CountyGEOID 16033 | 1,763.1 mi² | 1 mi² | 0.1% | 783 | 0.44 |
| 19 | Bonner CountyGEOID 16017 | 1,733.2 mi² | 184.9 mi² | 9.6% | 54,420 | 31 |
| 20 | Washington CountyGEOID 16087 | 1,452.9 mi² | 20.5 mi² | 1.4% | 11,583 | 8 |
| 21 | Power CountyGEOID 16077 | 1,403.8 mi² | 38.3 mi² | 2.7% | 8,246 | 5.9 |
| 22 | Adams CountyGEOID 16003 | 1,362.8 mi² | 6.7 mi² | 0.5% | 5,013 | 3.7 |
| 23 | Boundary CountyGEOID 16021 | 1,268.7 mi² | 9.4 mi² | 0.7% | 13,997 | 11 |
| 24 | Kootenai CountyGEOID 16055 | 1,237.8 mi² | 71.2 mi² | 5.4% | 191,864 | 155 |
| 25 | Lincoln CountyGEOID 16063 | 1,201.4 mi² | 4.5 mi² | 0.4% | 5,603 | 4.7 |
| 26 | Oneida CountyGEOID 16071 | 1,199 mi² | 1.5 mi² | 0.1% | 5,085 | 4.2 |
| 27 | Bannock CountyGEOID 16005 | 1,112.5 mi² | 35.6 mi² | 3.1% | 91,591 | 82 |
| 28 | Jefferson CountyGEOID 16051 | 1,093.7 mi² | 12 mi² | 1.1% | 35,297 | 32 |
| 29 | Latah CountyGEOID 16057 | 1,079.7 mi² | 0.9 mi² | 0.1% | 41,842 | 39 |
| 30 | Camas CountyGEOID 16025 | 1,074.2 mi² | 4.5 mi² | 0.4% | 1,316 | 1.2 |
| 31 | Ada CountyGEOID 16001 | 1,052.3 mi² | 8.5 mi² | 0.8% | 546,141 | 519 |
| 32 | Bear Lake CountyGEOID 16007 | 975.7 mi² | 73.9 mi² | 7% | 6,727 | 6.9 |
| 33 | Nez Perce CountyGEOID 16069 | 848.3 mi² | 8.2 mi² | 1% | 42,905 | 51 |
| 34 | Benewah CountyGEOID 16009 | 776.9 mi² | 7.3 mi² | 0.9% | 10,508 | 14 |
| 35 | Minidoka CountyGEOID 16067 | 757.2 mi² | 5.1 mi² | 0.7% | 22,911 | 30 |
| 36 | Gooding CountyGEOID 16047 | 729.3 mi² | 4.8 mi² | 0.7% | 16,446 | 23 |
| 37 | Franklin CountyGEOID 16041 | 663.1 mi² | 4.7 mi² | 0.7% | 15,889 | 24 |
| 38 | Jerome CountyGEOID 16053 | 597.5 mi² | 5 mi² | 0.8% | 26,362 | 44 |
| 39 | Canyon CountyGEOID 16027 | 587 mi² | 16.6 mi² | 2.8% | 275,123 | 469 |
| 40 | Gem CountyGEOID 16045 | 559.8 mi² | 4.8 mi² | 0.9% | 21,773 | 39 |
| 41 | Lewis CountyGEOID 16061 | 478.8 mi² | 0.9 mi² | 0.2% | 3,704 | 7.7 |
| 42 | Madison CountyGEOID 16065 | 469.3 mi² | 4.1 mi² | 0.9% | 55,172 | 118 |
| 43 | Teton CountyGEOID 16081 | 449.1 mi² | 1.1 mi² | 0.2% | 13,254 | 30 |
| 44 | Payette CountyGEOID 16075 | 406.9 mi² | 3.4 mi² | 0.8% | 27,824 | 68 |