By 1857 Osawatomie had grown to a town of 800 and in 1859 hosted the first convention of the Kansas Republican Party. In recognition for Osawatomie's part in ensuring Kansas remained a free state, the Kansas Legislature established the Osawatomie State Mental Hospital in 1863, the first mental hospital west of the Mississippi River. It admitted its first patient in 1866, and is still operational. By 1879, a railroad was built to serve Osawatomie, aiding its growth into a supply town and a main shipping point. As a result, Osawatomie grew to a population of 4,046 by 1910. Osawatomie was a division point for the Missouri Pacific Railroad and the Union Pacific Railroad from 1879 to 1985.