John H. Callahan (January 25, 1845 – March 13, 1914) was one of two men from the 122nd Illinois Volunteer Infantry Regiment to receive the Medal of Honor during the American Civil War. Callahan was a private in Company B. The medal was awarded for capturing a Confederate flag during the Battle of Fort Blakely on April 9, 1865; he was one of fourteen men awarded with the Medal of Honor at this battle. Callahan joined the Army in August 1862, and was mustered out in July 1865. He died on March 13, 1914 in Manhattan, Kansas and is buried in Sunset Cemetery.