[1] William P. Carlin was born at Rich Woods in Greene County, Illinois, and educated in the local schools.

[2] His uncle Thomas Carlin, a Jacksonian Democrat and veteran of the War of 1812 served as Illinois' governor when William was a boy.

Carlin was appointed a brevet second lieutenant in the 6th U.S. Infantry and assigned to duty on the Western frontier at Fort Snelling and other subsequent posts.

He then was involved in the Utah War in 1858 in a U.S. Army force led by Albert Sidney Johnston, a future Confederate general.

He participated in the Battle of Fredericktown on October 21, where his men help rout part of the Missouri State Guard under M. Jeff Thompson.

As a reward for his performance, in November Carlin took command of the Southeastern Missouri District, a post he held through the winter into early spring of 1862 when he was assigned to lead a brigade of infantry.

At the Battle of Bentonville on March 19, it conducted a "probing attack" that was routed by a major Confederate counterattack in which General Carlin narrowly escaped capture.

He wrote and published his autobiography, Memoirs of Brigadier General William Passmore Carlin, USA, which detailed his long career.