Fort Atkinson, established in 1820 on the recommendation of the Lewis and Clark Expedition, was one of the earliest U.S. military posts west of the Missouri River. The garrison held about 1,200 soldiers at its peak and operated until 1827. Reconstruction began in 1961 and took 20 years. The park has reconstructed barracks, gates, an armorer's shop, a council house, and the Sutler Store, plus the Harold W. Andersen Visitor Center. Visitors hike, picnic, and take historical tours. Living history demonstrations run the first weekend of each month from May through October, 10 a.m. to 4 p.m., and candlelight tours are held in November. Grounds are open sunrise to dusk. The visitor center is open Wednesday through Sunday, 10 a.m. to 4 p.m., from May 1 to October 9 and by appointment the rest of the year.