As the name indicates, Grand Mound State Park contains the largest remaining prehistoric Indian mound in the upper Midwest. It is estimated to have been built in 200 B.C. and later occupied by Middle and Late Woodland peoples. It was declared a National Historic Landmark and is also listed on the National Register of Historic Places. The mound was recently deemed to be an effigy mound in the shape of a muskrat. It is 140 feet wide, 100 feet wide, and 25 feet high. There are also four smaller, mounds at the site. The site is currently closed as of early 2016 but it appears that it might open in the coming years.
The park was privately owned beginning in 1930 to protect it. The owner sold it to the Minnesota Historical Society in 1971, which built a visitor center and opened the park in 1975. Concerns of Native Americans that the mounds should not be open to tourists, because they considered the mounds sacred burial grounds, prompted the park's closure in 2007. However, beginning in early 2015, this thinking had begun to change. Interest increased among all parties, including the Native Americans, that the history of the site and the ancient peoples who lived there should be told once again. Plans to reopen the site range from simple trails with interpretive panels to opening a the visitor center.