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.
Born in Decatur, Illinois, on March 19, 1873, he was the son of Illinois Governor Richard James Oglesby and Emma Gillet Oglesby, a member of the prominent Oglesby political family of Kentucky and Illinois. Oglesby served in the United States Army during the Spanish–American War and was a member of Illinois House of Representatives in 1905. He served as lieutenant governor for two non-consecutive terms, from 1909 to 1913 and from 1917 to 1921. (He ran for reelection after his first term in 1912 and was defeated).
Oglesby was a delegate to the Illinois convention to ratify the Twenty-first Amendment to the United States Constitution in 1933.
- 1908 Illinois lieutenant gubernatorial election
- 1912 Illinois lieutenant gubernatorial election
- 1916 Illinois lieutenant gubernatorial election