Charles R. Jennison was born on June 6, 1834 in Antwerp, Jefferson County, New York. His family moved to Wisconsin in 1846 where Jennison studied medicine. Marrying at 20 years old, Dr. Jennison moved to Osawatomie, Kansas in 1858 and to Mound City, Kansas shortly thereafter. Jennison was considered the most brutal jayhawkers. Whereas some other importnat leaders of irregulars in the Bleeding Kansas border conflict shared these traits, Jennison was different because he plundered for personal gain. Jennison worked with James Montgomery in opposing pro-slavery settlers and irregulars believed to be working with Border Ruffians.