Sheilagh Thompson was born on December 10, 1923 to Robert and Leah Thompson. She grew up in Southern California and graduated from San Pedro High School. She earned her BA in 1944, her MA in 1947, and her PhD in 1951 all in anthropology from the University of California, Berkeley. She married Richard Brooks on November 10, 1951, and the couple had two children, Kathleen and Carolyn.