Williamson was born in Columbia, Kentucky in 1829. When he was fifteen years old his family moved to Iowa, where he worked as a farmer, before studying law and being admitted to the bar. In the years prior to the Civil War he served as the chairman of the Iowa State Democratic Committee. When the Civil War began Williamson volunteered in the
4th Iowa Volunteer Infantry Regiment. Serving as a
first lieutenant he fought at the
battle of Pea Ridge where he was wounded on the first day of fighting there. On March 4, 1862, he was promoted to
lieutenant colonel and then on July 21, 1862, to
colonel of the 4th Iowa. Colonel Williamson and his regiment spent the fall of 1862 on garrison duty at
Helena, Arkansas. In December Williamson was part of
William T. Sherman's force which attacked the Confederate forces at the
Battle of Chickasaw Bluffs. Williamson was again wounded and for his services here was eventually awarded the Medal of Honor in 1895. Williamson recovered in time to take part in the
Vicksburg Campaign and the following
Siege of Vicksburg. After the fall of the city, he assumed command of the 3rd Brigade, 1st Division, XV Corps until September, 1863 then commanded the 2nd Brigade, 1st Division, XV Corps at the
Battle of Chattanooga. Williamson's division, commanded by
Peter J. Osterhaus was temporarily attached to the forces under
Joseph Hooker and took part in the
Battle of Lookout Mountain. The division was returned to the
Army of the Tennessee and Williamson led the 2nd Brigade during the
Atlanta campaign. At the
Battle of Jonesborough he was wounded in the hand. On December 19, 1864, he received a brevet promotion to
brigadier general of U.S. Volunteers, on January 13, 1865, a full promotion to brigadier general and on March 13, 1865, a brevet promotion to major general of volunteers. Briefly during the summer of 1865 he commanded the District of St. Louis and was mustered out of the volunteer service on August 24, 1865, but was on an inspection tour of army posts in the West and did not find out until he returned in October 1865. In 1864 Williamson had been elected chairman of the Iowa delegation to the National Republican Convention in Baltimore, but did not attend due to duty to the army. After the War he resumed his law practice in Iowa. He served as Commissioner of the
United States General Land Office from 1876 to 1881. During this time he served as chairman of the Public Land Commission, which was created by Congress in 1879. He later became President of the Atlantic & Pacific Railroad. He was a companion of the New York Commandery of the
Military Order of the Loyal Legion of the United States. He was in
Jamestown, Rhode Island when he died on September 7, 1902. ==Medal of Honor citation==