Boise, capital and largest city of Idaho, U.S., and the seat (1864) of Ada county. It lies along the Boise River in the southwestern part of the state. Because mountains to the north protect it from Canadian blizzards, Boise has relatively mild winters, as well as hot, dry summers.

Boise was named by early 19th-century French Canadian trappers for the tree-lined river (French boisé, “wooded”) that provided relief for travelers crossing the desolate Snake River plain. Following the 1862 gold rush to the Boise River basin, Fort Boise was established (July 4, 1863), and a community developed to provide services for the nearby mines. Its location at the crossroads of the Oregon Trail and the routes to the Boise Basin and Owyhee mines ensured Boise’s early growth, and it became the capital of Idaho in 1864. After 1902 the Boise Irrigation Project built nearby Arrowrock Dam and several other dams on the Boise River to provide the region with water storage and recreational facilities. Agricultural expansion and the growth of a commercial lumber industry contributed to Boise’s rapid growth in the early 20th century. One of the world’s largest construction companies also grew up there.

The city’s diversified industries now include agriculture (fruit, sugar beets, and livestock), lumbering, electronics, and wholesale trade and trucking. Growth in the high-tech industries around Boise accounted for much of the city’s increase in population during the 1990s. Federal and state government agencies also provide much local employment. Boise’s numerous city parks contain specimens of trees from all over the world, many planted by U.S. presidents and visiting dignitaries. Buildings of historical interest include the Assay Office (1871), Old Idaho Penitentiary (built c. 1870, closed 1973), and the Idaho Historical Museum (1907). The city is the headquarters of Boise National Forest, which is dotted with abandoned mines and ghost towns. Boise State University was founded in 1932 as a junior college. Inc. 1864. Pop. (2010) 206,100; Boise City–Nampa Metro Area, 616,561; (2020) 235,684; Boise City Metro Area, 764,718.

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The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Michele Metych.

Idaho, constituent state of the United States of America. It ranks 14th among the 50 U.S. states in terms of total area. Its boundaries—with the Canadian province of British Columbia to the north and the U.S. states of Montana and Wyoming to the east, Utah and Nevada to the south, and Oregon and Washington to the west—are both historical and geographic in derivation. The boundary with British Columbia follows the 49th parallel of north latitude, while the border with Utah and Nevada follows the 42nd parallel; both lines were established by treaty—the northern between the United States and Britain in 1846 and the southern between the United States and Spain in 1819. The border with Montana follows the Continental Divide, while the border with Wyoming incorporates a small slice of Yellowstone National Park. Idaho’s border with Oregon and Washington is a 480-mile (770-km) straight stretch except between the Idaho cities of Weiser and Lewiston, where Hells Canyon of the Snake River serves as a natural boundary. Boise is the state capital.

Idaho, admitted as the 43rd state of the union on July 3, 1890, is one of the Mountain states, but it is often classified as part of the Pacific Northwest, a region unified by the Continental Divide as an eastern boundary and by the Columbia River drainage basin, which covers virtually the entire area. The name Idaho is thought to be derived from a Shoshone phrase meaning “gem of the mountains.”

Quick Facts
Idaho: flag
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See article: flag of Idaho
state seal of Idaho
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Seal of Idaho
Idaho's state bird is the mountain bluebird.
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Idaho's state bird is the mountain bluebird.
Idaho's state flower is the syringa, or mock orange (Philadelphus lewisii).
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Idaho's state flower is the syringa, or mock orange (Philadelphus lewisii).
Capital:
Boise
Population1:
(2020) 1,839,106; (2024 est.) 2,001,619
Governor:
Brad Little (Republican)
Date Of Admission:
July 3, 1890
U.S. Senators:
Mike Crapo (Republican)
James E. Risch (Republican)
State Nickname:
Gem State
State Motto:
"Esto Perpetua (Let It Be Perpetual)"
State Bird2:
mountain bluebird
peregrine falcon
State Flower:
Lewis’ mock orange (‘syringa’)
State Song:
“Here We Have Idaho”
Seats In U.S. House Of Representatives:
2 (of 435)
Time Zone:
Pacific (GMT − 8 hours)
Mountain (GMT − 7 hours)
Total Area (Sq Km):
216,443
Total Area (Sq Mi):
83,569
  1. Excluding military abroad.
  2. The peregrine falcon is the state raptor.

Idaho is shaped much like a logger’s boot, thereby accidentally reflecting the state’s rugged forested and mountainous terrain in which logging and mining play major roles. The residents of Idaho enjoy some of the largest unspoiled natural areas in the United States, including about 3,900 square miles (10,000 square km) of wilderness and primitive land in which roads and vehicles are seldom to be found. Since its development in 1936 Sun Valley has become an internationally known area for winter sports. Idaho also has large supplies of groundwater. Hot springs are found in many parts of the state and are used to heat some homes and buildings in Boise, whose name (French boisé, “wooded”) reflects its settlement as an oasis for explorers who once crossed the desolate Snake River Plains. A frontier character is still evident in the individualism of voting that makes the crossing of party lines a frequent occurrence in an otherwise fairly conservative climate. Area 83,569 square miles (216,443 square km). Population (2020) 1,839,106; (2024 est.) 2,001,619.

Land

Diversity of the natural environment is characteristic of Idaho’s landscape, creating a sectionalism that is reflected in the state’s community life, politics, economy, and cultural development, as well as in the varieties of its soils and animal and plant life. Elevation is often a more important factor in controlling Idaho’s climate than is latitude. The northern areas of the state are lower in elevation on the average than are much of the central and southern areas. Prevailing westerly winds from the Pacific Ocean blanket most of the state, especially the northern and southwestern regions. A drier, colder, continental climate is more noticeable in the southeastern counties, but Idaho has a milder climate than most of the states located in the same latitudes east of the Continental Divide.

Relief and drainage

Parts of four major physiographic provinces are included within Idaho: the Northern Rocky Mountains, the Middle Rocky Mountains, the Columbia Basin, and the Basin and Range Province. The Northern Rockies extend from the Canadian border to south-central Idaho and occupy nearly half the state’s area. Peaks reaching elevations between 10,000 and 12,000 feet (3,000 and 3,700 metres) are common in central Idaho. At 12,662 feet (3,859 metres) in the Lost River Range, Borah Peak is the state’s highest point. Other notable ranges in this part of the state include the Sawtooth, Pioneer, Continental Divide, Beaverhead, and Bitterroot. Peak elevations generally decrease northward to about 6,000 feet (1,800 metres) at the Canadian border.

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The Middle Rocky Mountains occupy a narrow strip along the Idaho-Wyoming border. The area comprises several ranges that trend north-south and northwest-southeast and rise to between 7,000 and 10,000 feet (2,100 and 3,000 metres). Grass- and sagebrush-covered plateaus and valleys and a few small lakes are found between the ranges.

The Basin and Range Province extends into southeastern Idaho as a roughly triangular-shaped desert with its base along the Idaho-Utah border. A series of low north–south-trending block-faulted ranges separate small gravel-floored basins.

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The remainder of the state is included within the Columbia Basin, which in Idaho is occupied entirely by the arid Snake River plateau. The Snake River follows the plateau in a broad crescent across southern and western Idaho. Next to the Northern Rocky Mountains, it is the major natural feature of the state. It rises in the southeastern part of the state, with tributaries in Yellowstone National Park, and flows from east to west through “sagebrush Idaho.” With huge reclamation projects, the river valley contains most of Idaho’s irrigated farmland. The course of the Snake River includes Hells Canyon—at 7,900 feet (2,400 metres) North America’s deepest gorge—and 212-foot- (65-metre-) high Shoshone Falls. Its valley is a geologically complex sequence of lakes, lava beds, mesas, buttes, canyons, and desertscape, symbolized by the barren craters and cones of the Craters of the Moon National Monument.

Idaho has some 2,000 lakes, and water is the state’s greatest single resource. A major portion of its industry, agriculture, and population lies along the Snake River, which furnishes water in abundance for one of the country’s largest irrigated areas and developed hydroelectric power sources.