William P. Carlin was a native of Illinois and the nephew of Thomas Carlin, the sixth Governor of Illinois. William Passmore Carlin graduated from West Point in 1850.

He was assigned to the 6th United States Infantry, and spent the next 10 years fighting the Plains Indians and on frontier garrison duty. He fought against the Sioux in 1855 in the expedition lead by General William S. Harney, in the 1857 campaign against the Cheyenne headed by Colonel Edwin V. Sumner, and in the campaign against the Mormons in Utah in 1858, led by General Albert Sidney Johnston.

When the Civil War started in 1861, he was a Regular Army Captain, but was soon detailed to the Volunteer service as Colonel and commander of the 38th Illinois Volunteer Infantry (being commissioned on August 5, 1861). The Regular Army-like regimen he implemented with his troops caused no end of consternation amongst the men, but was responsible for instilling the discipline needed to mold it into an effective fighting force. Posted in Missouri, he participated in his first pitched battle on October 21, 1861, when his men routed a Confederate force under Missouri Militia General Jeff Thompson at Fredericktown. In November that year he was given command of the Southeaster Missouri District, holding that position until March 1862. Advanced to brigade command, he led his men in the October 1862 Battles of Corinth, Mississippi and Perryville, Kentucky (where he drew accolades from his superiors for leading a charge that swept the Confederates from the field). Promoted to Brigadier General, US Volunteers on November 29, 1862, he participated in a number of smaller skirmishes leading up to the December 1862 Battle of Murfreesboro, where his brigade suffered heavy casualties. From January 1863 to August 1864 he commanded the 1st Brigade of the 1st Division of the XIV Corps in nearly every battle the Union Army of the Tennessee was involved in, which encompassed the engagements at Tullahoma, Chickamauga, Lookout Mountain, Missionary Ridge, Chattanooga and the summer 1864 Atlanta Campaign. Advanced to command of the 1st Division of the XIV Corps, he led it in the Union victory at the September 1, 1864 Battle of Jonesboro, Georgia, Sherman’s March to the Sea, and the Campaign through the Carolinas. In the March 1865 Battle of Bentonville, North Carolina, his Division bore the brunt of the last offensive movement by the Confederate Army of Tennessee. Outnumbered and out-positioned, it was routed and crushed by the onslaught of the Confederate charge that opened the main engagement. General Carlin himself was conspicuous at the front lines, and found himself at one point alone and exposed, narrowly escaping capture twice. Despite the defeat of his Division, he retained his command until the end of the war.

During his volunteer service he received numerous brevets in both the Regular Army and Volunteers, and ended with brevets of Major General in each respective service. Mustered out of the Volunteers, he reverted to his Regular Army rank of Major in the 16th United States Infantry. From 1867 to 1868, he served as the assistant commissioner of the Tennessee Freedman’s Bureau, then served the next 25 years in various garrisons and commands, retiring in 1893 with the rank of Brigadier General, US Army.

In 1903 he passed away while traveling on board a train in Whitehall, Montana, and he was buried in his hometown of Carrollton, Illinois.

The town of Carlin, Nevada is named for him, gaining the sobriquet when he was stationed there during the 1858 Mormon Expedition.