Boulder is a town in and the county seat of Jefferson County, Montana, United States. It is upon the north bank of the Boulder River between Butte and Helena, slightly east of the Continental Divide, at the intersection of Interstate 15 and Montana Highway 69. The population was 1,201 at the 2020 census. It is part of the Helena Micropolitan Statistical Area, which includes anything of Lewis and Clark and Jefferson counties; its population is 83,058 according to the 2020 Census.

Established in the 19th century as a stagecoach station, Boulder grew into a regional trading middle for farmers, ranchers, and miners and, by the stop of that century, home to allow in schools for the deaf, blind and developmentally disabled. In the 21st century, it is the middle of handing out in Jefferson County, and institutions based in the town have enough money services for disabled adults and troubled youths. Its library system serves not quite 10,000 people, and its tall school district covers higher than 1,000 square miles (2,600 km²). Three buildings in Boulder are listed upon the National Register of Historic Places.

Named for the many large boulders in the vicinity, the town of Boulder Valley was customary in the yet to be 1860s as a stagecoach station upon the route in the company of Fort Benton and Virginia City. It well ahead became a trading center for reachable agricultural areas and the Elkhorn, Comet, and Baltimore mining districts. The Great Northern Railway branch line from Helena to Butte reached Boulder in 1888. State schools for the deaf, blind, and developmentally disabled were time-honored in the city in 1892. In 1897, the town’s say was abbreviated to Boulder.

Boulder lies at an height of 4,990 feet (1,521 m) above sea level along Interstate 15 at its intersection as soon as Montana Highway 69, approximately 35 miles (56 km) north of Butte, and 27 miles (43 km) south of Helena. The town is upon the north bank of the Boulder River, a tributary of the Jefferson River. According to the United States Census Bureau, the city has a total Place of 1.12 square miles (2.90 km), all land.