Free Admission. Dacotah Prairie Museum is Brown County’s premier history museum. Over the decades the Museum has been a storehouse for the county’s collective memory and has provided exceptional archival, research, exhibit and educational services. The Museum is housed in the historic Northwestern Bank building built in 1889, a cornerstone of Aberdeen’s vibrant downtown district. Exhibits on display highlight Brown County’s history and the people who lived here past and present. Art exhibits by local artists rotate through the galleries on a regular basis as well as traveling STEM and history exhibits.