Boise (locally /ˈbɔɪsi/ , also /bɔɪzi/) is the capital and most populous city of the U.S. state of Idaho. Boise is the county seat of Ada County. The population of the city was 235,685 at the 2020 census. The Boise metropolitan area, also known as the Treasure Valley, includes five counties of Idaho with an estimated population of 846,000, the most populous metropolitan area in Idaho and 74th-most populous in the United States.
Located on the Boise River in southwestern Idaho, it is 41 miles (66 km) east of the Oregon border and 110 miles (177 km) north of the Nevada border. Downtown Boise's elevation is 2,704 feet (824 m) above sea level. Originally established as a military outpost in 1863 during the gold rush era, Boise rapidly grew due to its location on the Oregon Trail and its proximity to mining operations in the surrounding region. By the late 19th century, it had become a commercial and transportation hub, bolstered by the arrival of the railroad and irrigation projects that supported agriculture in the Treasure Valley.