She later moved to Cheyenne, where she graduated from Cheyenne Central High School, and thereafter from Northwestern University in Evanston, Illinois.
Her best-known book is a history of the Cheyenne Frontier Days rodeo, a popular event held annually since 1897. She was instrumental in the founding of the Cheyenne Frontier Days Old West Museum. Born in Spokane, Washington, Flynn was the oldest of four children of John Edward Smith and the former Ethel Valentine Grammer, who wed in Nebraska in 1928.
Shirley Flynn was a member and secretary for the founding board of the Cheyenne Frontier Days Old West Museum, which opened in 1978 in a temporary cinderblock building.
Flynn was the director of the museum from 1987 to 1991, during which time she helped to oversee the expansion of the museum in 1992. In 1980, Flynn researched and played the role of Mary Todd Lincoln in the first docudrama of the Old West Museum.
She also lectured at schools, civic groups, clubs, and historical societies. In 1996, Flynn authored Let"s Go! Let"s Show! Let"s Rodeo! The History of Cheyenne Frontier Days which chronicles the history of the event from its inception in 1897.
According to the Wyoming Tribune Eagle, she is considered an authority on the history of the rodeo and was a consultant for documentaries on the event.
She wrote Cheyenne Frontier Days, a work published in 1999 by the Wyoming State Library. She penned articles for The Annals of Wyoming, the magazine of the Wyoming Historical Society, including "Wyoming Portrait: Renesselaer Schuler Van Tassel" (spring 1999) and "Cheyenne"s Harry P. Hynds: Blacksmith, Saloon Keeper, Promoter, Philanthropist" (summer 2001). L. Michael McCraken, the president and publisher of The Wyoming Tribune Eagle, considered the award to Flynn to be particularly fitting because she had served as a consultant to the newspaper when the award was established in 1998.
Flynn was also named to the "Roll of Honor" of the National Society of the Colonial Dames of America.
Flynn died in 2013 at the age of eighty-four in a hospice in Cheyenne.
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