Quincy, Illinois, merchant, attorney, and soldier. Belleville, Virginia, native. Married to Margaret A. Prentiss. Father of Harrison T. Prentiss, Guy C. A. Prentiss, Martha R. Prentiss, Jacob H. Prentiss, Ella Prentiss, Benjamin M. Prentiss, Jr., Clay Prentiss, and Joseph Prentiss. Rope-walk worker in Marion County, Missouri, from 1836 to 1841. Veteran of the U.S.-Mexican War. Rope-maker in Quincy, Illinois, in 1850. Forwarding merchant in Quincy in 1860. Served in the 10th Illinois Volunteer Infantry Regiment (U.S.A.) as colonel from April 1861 to August 1861. Served as brigadier general of volunteers in the U.S. Army from May 1861. Captured at the Battle of Shiloh on April 6, 1862 and exchanged in October 1862. Commanded the Easter District of Arkansas at Helena, Arkansas, as major general from March 1863 to October 1863. Resigned from the U.S. Army in October 1863. Attorney in Quincy from 1863.