[1] Irwin had an interest in natural history and while at Fort Buchanan, Arizona, in 1858–1860 he collected reptile specimens for the Smithsonian Institution.

[3] A collection of his papers is held at the National Library of Medicine [4] Irwin was born in County Roscommon, Ireland, and immigrated with his parents to the United States in the 1840s.

Second Lieutenant George Nicholas Bascom led a group of 60 men from the 7th Infantry after Cochise but was soon besieged, prompting a rescue mission by the army.

[5] The Irwin-Bascom matter is dramatized in the 1966 episode, "The Hero of Apache Pass", on the syndicated television anthology series, Death Valley Days, hosted by Robert Taylor.

The actor Charles Bateman was cast as Irwin; Phillip Pine as Colonel Pitts, Dick Simmons as Bascom, and Don Keefer as the commandant.

[8] His son George LeRoy Irwin (graduated from West Point in 1889) served in World War I and became a Major General in the Army.

His grandson Stafford LeRoy Irwin (graduated from West Point in 1915) served in World War II and became a Lieutenant General in the Army.