Fort Steilacoom was founded by the U.S. Army in 1849 near Lake Steilacoom. It was among the first military fortifications built by the U.S. north of the Columbia River in what was to become Washington. Fort Steilacoom was decommissioned as a military post in 1868. In 1871 an insane asylum opened there, with the barracks serving as patient and staff housing. Initially referred to as the "Insane Asylum for Washington Territory" the hospital was latter named Western State Hospital. Hospital residents grew crops and orchards in the park area, and planted many of the poplar trees that line the lake shore. More than 3,000 hospital residents are buried in the cemetery near the parking lot.