Fort Osage was an early 19th century factory trading post system located in present day Sibley. It was one of three forts created by the U.S. Army in an attempt to establish control over the newly acquired Louisiana Purchase territories. The fort ceased operations in the 1820s and fell into disrepair and ruin. Archeologists rediscovered Fort Osageâ™s foundations in the 1940â™s, and a replica of the fort was rebuilt between 1948 and 1961, to portray Fort Osage as it was in 1812.