The question has a false floor in it: Idaho is not inside a state, it is one. The Congressional Research Service lists Idaho as the 43rd state, admitted on 3 July 1890. The name also belongs to places inside the state — the federal time-zone rules run a boundary along the line between Idaho County and Lemhi County, both of them counties of Idaho — which does nothing to make the question easier. What follows is the geography the question is usually reaching for. If you came looking for the history instead, start with when Idaho became a state.
Which region it is in
Two official answers, both correct, because federal bodies draw the line differently for different purposes. The U.S. Census Bureau puts Idaho in Region 4, the West, and Division 8, the Mountain division, alongside Montana, Wyoming, Nevada, Utah, Colorado, Arizona and New Mexico. Federal power law reaches the other way: 16 U.S.C. 839a defines the Pacific Northwest as Oregon, Washington and Idaho, plus Montana west of the Continental Divide and the parts of Nevada, Utah and Wyoming inside the Columbia River basin. Idaho is in the Mountain West by census geography and in the Pacific Northwest by the statute that governs its electricity.
Who it borders
Six states and one Canadian province. The Idaho Office of Emergency Management’s state profile lists them: Montana on the northeast, Wyoming on the east, Utah and Nevada on the south, Oregon and Washington on the west, and British Columbia on the north. The same profile records the range of the ground between them: 738 feet above sea level at the Snake River in Lewiston to 12,662 feet at the summit of Borah Peak.
Capital and largest city
Boise, on both counts. Article X, Section 2 of the Idaho Constitution placed the seat of government at Boise City for twenty years from admission, after which the legislature could put a move to a statewide vote; the Idaho Capitol Commission still gives the capital as Boise. It is also the largest city: the 2020 Census counted 235,684 people inside the city limits, against 117,635 in Meridian next door. Boise is the seat of Ada County.
Two time zones
Idaho is split. Under 49 CFR 71.9 the line between the Mountain and Pacific zones enters Idaho at the Canadian border, runs south along the Montana line to the Idaho County–Lemhi County boundary, then southwest to the Salmon River and west along that river to the Oregon line. North and west of that line is Pacific time; the rest of the state, Boise included, is Mountain. What time it is in Boise sets out how that works day to day.
Area and population
Idaho covers 83,569 square miles, of which 82,643 is land and 926 water, in the Census Bureau’s state area measurements. In that table, thirteen states are larger by total area and ten hold more land. The 2020 Census counted 1,839,106 people in Idaho, and the Census Bureau’s estimate for 1 July 2025 put the figure at 2,029,733 — 37th among the 50 states in that year’s estimates, between New Mexico and Nebraska. Boise’s own numbers are on the population page.