Boulder is a town in and the county seat of Jefferson County, Montana, United States. It is on 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 1,183 at the 2010 census. It is part of the Helena Micropolitan Statistical Area.
Established in the 19th century as a stagecoach station, Boulder grew into a regional trading center for farmers, ranchers, and miners and, by the end of that century, home to state schools for the deaf, blind and developmentally disabled. In the 21st century, it is the center of government in Jefferson County, and institutions based in the town offer services for disabled adults and troubled youths. Its library system serves about 10,000 people, and its high school district covers more than 1,000 square miles (2,600 km2). Three buildings in Boulder are listed on the National Register of Historic Places.