Henry J. Reilly (1881–1963) was an American soldier and journalist. The son of an artillery officer who died in the 1900 Battle of Peking, Reilly graduated from West Point in 1904. During World War I, he commanded the 83rd Infantry Brigade of the 42nd ("Rainbow") Division in combat in France. After the war, he edited the Army and Navy Journal from 1921 to 1925. He wrote several books, including Why Preparedness? (1916), based on what he had seen on Europe's eastern and western fronts in 1914 and 1915; America's Part (1926); and Americans All: History of the Rainbow Division (1936), which described the division's military actions, including stories about soldiers and officers from private to general.