The Thomas K. Harrelson World War II Collection primarily relates to Harrelson's World War II service as an aviation mechanic and also provides a glimpse into his 30-year service with the U.S. Air Force, from 1938 to 1968. It is comprised mostly of textual materials but does include a small amount of visual materials. Materials have been arranged chronologically.

The bulk of the materials relate to Harrelson's service during World War II. These include special orders, Harrelson's military biographical sketch, a photocopy of mission timelines, military awards, and discharge paperwork. Also present is a torn propaganda flier in German. It states "Hitler erklate krieg an die vereinigten staaten am, December 11, 1941" and includes a section of a July 1, 1943 speech by President Roosevelt, also in German. Twenty-five photographs are also present, including portraits of Harrelson; a March 1944 group portrait of the 358th Bomb Squadron, Engineering Section; and three unidentified military personnel in front of obscured aircraft "Princess Pat," likely a Boeing B-17. There are also three prints that depict damage to an aircraft wing. A highlight of the collection related to Harrelson's World War II service are the pocket atlas and 10 maps annotated with handwritten notes documenting bombing missions over France and Germany that he supported.

A few items pertain to Harrelson's pre-World War II service, including a yearbook for the North Carolina National Guard, and holiday menus from Fort Bragg. Thirteen prints depict many unidentified military personnel with military vehicles among mountains and posing in front of large redwood trees in an unidentified location, possibly during his National Guard service.

The collection also holds personal materials, including two 1941 recommendations letters on behalf of Harrelson, a membership letter and certificate for Operation Golden Eagle, clippings about Harrelson and his rockhounding hobby, Harrelson's obituary, and assorted items relevant to the 50th anniversary of the Boeing B-17, including an event program, decal and group photograph of unidentified men, likely inluding Harrelson. A few pieces of ephemera are present, including a poem titled "The Forgotten Man" by an unknown author and a satirical "Wanted!" flier from the Old City Jail of Tucson, Arizona for the "Harrelson Gang." Seven photographs are present, including three black-and-white prints that depict Harrelson, likely with family members, in 1972. Also present are three undated color images of two men and a young lady in front of a scoreboard at Tom Harrelson Field, possibly in Colorado, and a 1989 color print of two men in front of a docked aircraft carrier.

Some photographic prints include captions or inscriptions that provide limited contextual information, such as names, locations, and dates. Most of the prints are black-and-white, although four are in color. Sizes vary from 2x4-inches to 8x10-inches.