It collects and interprets the history and culture of the St. Vrain Valley in northern Colorado.
[2] In 2015 the museum expanded its premises, an expansion including the 250-seat Stewart auditorium, an atrium, and education center.
[3] The Longmont Museum has two permanent exhibits, the Longs Peak Room Interactive Gallery and Front Range Rising, both of which explore the history of Longmont and the northern Colorado Front Range region.
Major recent exhibitions have included Return to Route 66: Photographs from the Mother Road, Ansel Adams & Edwin Land: Art, Science and Invention – Photographs from the Polaroid Collection; and Edward Weston: Life Work.
The Longmont Museum hosts a Día de los Muertos celebration each year, bringing in over 1,500 people to see altars from the community, hear traditional music, and try pan de muertos and other traditional foods eaten on Día de los Muertos.