John Gillett Oglesby (March 19, 1873 – May 27, 1938) was the 29th and 31st Lieutenant Governor of Illinois from 1909 to 1913, during this time he served under Governor Charles S. Deneen, and again from 1917 to 1921 serving under Governor Frank O. Lowden. He was a candidate in the Republican primary for governor in 1920 and in 1936. Oglesby was a delegate from Illinois to the Republican National Conventions in 1920, 1924, 1928, and 1932. Oglesby was a delegate to the Illinois convention to ratify the Twenty-first Amendment to the United States Constitution in 1933.