Cedar Valley Seminary (Mitchell County Historical Museum) is a historic seminary building at N. 6th and Mechanic Streets in Osage, Iowa.It was built in 1869 and added to the National Register of Historic Places in 1977.The school was founded at Osage, as a Baptist academy, in 1862, by the joint efforts of Rev. Alva Bush, the citizens of Osage, and the Cedar Valley Baptist Association. On Monday morning, January 12, 1863 Prof.