This regiment was raised largely through the influence and exertions of Samuel A. Rice, late attorney-general of the state. Four companies were recruited in Mahaska county, three in Keokuk and three in Marion.
They went into camp in August, 1862, at Oskaloosa, and on the first of October were mustered into the service.
The field officers were Samuel A. Rice, colonel; Cyrus H. Mackay, lieutenant-colonel and Hiram D. Gibson, major.
The regiment left for the seat of war in November; went to St. Louis, from there to Columbus, Ky. In January, 1863, it was sent to Helena, Ark., where, in June, Colonel Rice took command of a brigade, and from that date Lieutenant-Colonel Mackay commanded the regiment.
At the battle of Helena, where 15,000 confederates under General Holmes attacked the city, the Thirty-third was first brought into action. It was in an exposed position, made an excellent fight in support of two batteries, and captured a large number of prisoners. Colonel Rice commanded the brigade to which it was attached.
In April the brigade was with General Steele in his expedition toward the Red river, and had several engagements with the enemy. Upon his retreat, the battle of Jenkins' Ferry was fought, on the 29th, and it was here that General Rice received a wound in his foot which proved fatal. In this battle the Thirty-third lost 129 men. Colonel Mackay was severely wounded and the command of the regiment devolved on Captain Boydston. Major Gibson, who had resigned, was captured at Mark's Mills. The regiment went to Little Rock in November, where it remained until February, 1865, when it joined the expedition against Mobile, taking an active part in that brilliant campaign. Soon after it returned to Iowa and was mustered out.
SOURCE, Benjamin F. Gue, Biographies And Portraits Of The Progressive Men Of Iowa, Volume 1, p. 114