The MonDak Heritage Center is located in a building that was completed in 1984 and features a permanent gallery that focuses on the history of eastern Montana communities along with a gallery that highlights the work of J.K. Ralston and other local artists. Prior to this time, local residents operated the J.K. Ralston Museum and Art Center in Sidney's former hospital starting in 1972. That museum operated for twelve years and was superseded in 1984 by the MonDak Heritage Center which offers a variety of exhibits related to the history and culture of the area along with art galleries and a research library.
Sidney was named in honor of Sidney Walters, the son of a local pioneer family. The community and is located about a mile west of the Yellowstone River and is six miles south of fort established by John Jacob Astor in 1828. The museum offers exhibits that share the history of these fur trading forts and other early settlements as well artifacts and information about the Native tribes that inhabited the area at that time and in the centuries that preceded Astor and Lewis and Clark's Corps of Discovery that arrived in the area in 1805.