Harry Preston Ilsley (December 7, 1884 – February 18, 1953) was an American jurist who served as a justice of the Wyoming Supreme Court from January 7, 1952, until his death.^[1]

Born in Markesan, Wisconsin, he was raised by an aunt and uncle because his parents died at an early age.^[2] He attended high school in Deadwood, South Dakota, and graduated from the University of South Dakota School of Law in June 1908.^[2] He was admitted to the South Dakota Bar and practiced law in Belle Fourche, South Dakota, until June 1910, when he moved to Sundance, Wyoming.^[2] He was admitted to the Wyoming State Bar and practiced law in Sundance until 1920, when Governor Robert D. Carey appointed him to serve as a Wyoming state district court judge.^[2] He served two years of an unexpired term and was then elected to five successive six-year terms.^[2] On January 7, 1952, Governor Frank A. Barrett appointed him to the Wyoming Supreme Court to fill the unexpired term of retiring Chief Justice of the Wyoming Supreme Court Ralph Kimball.^[2] In 1952, he was elected for a full six-year term on the Wyoming Supreme Court.^[2] He died in office on February 18, 1953.^[2] His son, John, practiced law in Gillette, Wyoming and later served as a district court judge on the Fourth Judicial District Court in Sheridan, Wyoming.^[2]