From
http://www.infoplease.com/ipa/A0004626.html :
Highest Ranking Officers in U.S. History
General and Commander-in-Chief(1)
George Washington (1732–1799), b. Westmoreland County, Va., unanimously voted by Congress on June 15, 1775, to the rank of general and commander-in-chief (of the Continental Army).
General of the Armies(2)
John Joseph Pershing (1860–1948), b. Linn County, Mo., made permanent general of the armies 1919.
General of the Army, General of the Air Force (Five-Stars)
George Catlett Marshall (1880–1959), b. Uniontown, Pa., promoted December 1944.
Douglas MacArthur (1880–1964), b. Little Rock, Ark., promoted December 1944.
Dwight David Eisenhower (1890–1969), b. Denison, Texas, promoted December 1944.
Henry Harley Arnold (1866–1950), b. Gladwyne, Pa. Arnold had the unique distinction of being a five-star general twice—in 1944 as general of the army, and in June 1949 as general of the air force. He is the only air force general to have held the five-star rank.
Omar Nelson Bradley (1893–1981), b. Clark, Mo., promoted September 1950.
Fleet Admiral (Five-Star)
William Daniel Leahy (1875–1959), b. Hampton, Iowa, promoted December 1944.
Ernest Joseph King (1878–1956), b. Lorain, Ohio, promoted December 1944.
Chester William Nimitz (1885–1966), b. Fredericksburg, Texas, promoted December 1944.
William Frederick Halsey (1882–1959), b. Elizabeth, N.J., promoted December 1945.
1. On March 15, 1978, George Washington was promoted posthumously to the newly created rank of General of the Armies of the United States. Congress authorized this title to make it clear that Washington was the army's senior general.
2. General Pershing was given the option of five stars but he declined. Source: Department of Defense and U.S. Army Historian, Research and Analysis Center.