Idaho vs Montana

The two states, county by county

Both maps share one density scale, so the same shade means the same number of people per square mile on either side of the border. Darker counties are denser. Select a county to open its page.

Side by side

Population and density

Idaho has 2,001,619 residents, 76% more than Montana's 1,137,233. Idaho ranks 38th and Montana 43rd of the 50 states and DC. Idaho is the more crowded, with 24.2 people per square mile against 7.8, 3.1 times.

Land area

Montana has 145,550 square miles of land, 76% more than Idaho's 82,645. The largest county-equivalent in Idaho is Idaho County at 8,478 square miles; in Montana it is Beaverhead County at 5,543.

Counties

Montana is divided into 56 county-equivalents and Idaho into 44, so an average Montana county covers 2,599 square miles against 1,878. The typical county in Idaho has 15,019 residents, against 7,814 in Montana. The most populous are Ada County (535,799) and Yellowstone County (171,583).

7 county names appear on both sides of the border: Blaine, Custer, Jefferson, Lincoln, Madison, Teton, Valley. Use the FIPS code, not the name, when joining data across the two states.

Household income

The median county in Idaho has a household income of $67,254, 13% above Montana's $59,534. The highest county incomes are Teton County ($94,895) in Idaho and Gallatin County ($90,942) in Montana, from SAIPE 2023.

Capitals and daylight

Boise and Helena are 290 miles apart in a straight line; from Boise the initial bearing is 43°, NE. On June 21, 2026, Boise gets 15 h 26 min of daylight and Helena 15 h 50 min; on December 21 the figures are 8 h 56 min and 8 h 34 min. Month by month tables are on the Boise and Helena daylight pages.

Where they sit

Both are in the Census Mountain division of the West region. By county internal points, Idaho spans 2 UTM zones and Montana 3.