The 31st Regiment Illinois Volunteer Infantry, nicknamed the "Dirty-First," was an infantry regiment that served in the Union Army during the American Civil War.

Among the early officers was Major Andrew J. Kuykendall, later a U.S. Representative and Illinois State Senator.

The regiment was mustered out on July 19, 1865, and discharged at Springfield, Illinois, on July 31, 1865.

The regiment suffered 9 officers and 166 enlisted men who were killed in action or who died of their wounds and 1 officer and 293 enlisted men who died of disease, for a total of 471 fatalities.

This article about a specific military unit of the American Civil War is a stub.