Alexander Thibeau was an American long-distance runner who, along with Albert Corey and Sidney Hatch, was one of Chicago's most prominent marathoners in the early 1900s.

[3] On June 30, 1906, 50,000 spectators saw Thibeau finish three minutes behind Thomas J. Hicks to place second in a marathon at an Amateur Athletic Union meet in Chicago.

[1][6][7][8] On May 2, 1908, in St. Louis, Missouri, Thibeau placed third behind Hatch and Forshaw with a 2:37:46 performance in a 25-mile marathon to earn a spot on the United States Olympic Team.

[7] The official report of the 1908 Summer Olympics indicates that Thibeau was one of twelve athletes selected to represent the United States in the marathon held on July 24, 1908, but there is no record that he participated in the event.

[14] On May 24, 1909, Thibeau turned professional in order to compete for $10,000 in prize money at an "international marathon derby" in Chicago on featuring eight of the "world's best long distance runners".