Ridder was born Kathleen Marie Culman on October 2, 1922, in New York City. Her father was a stockbroker who went broke during the Great Depression, and her mother worked in a dress shop to support the household. Ridder was active in sports in her youth, attended the all-girls Brearley School, and later went to Smith College. After college she married Robert Ridder, who was part of the family which founded Knight Ridder media company, and moved with him to Minnesota in 1943. She resided in Duluth with her husband while she completed a teacher's degree at the University of Minnesota Duluth, then relocated to Saint Paul.
In 1983, Ridder established the first endowment awarded to a female student-athlete at the University of Minnesota, known as the Kathleen C. Ridder scholarship for studies in math, medicine, or science. The University of Minnesota also awards the "Kathleen C. and Robert B. Ridder Scholarship" annually to a student athlete on the Golden Gophers women's ice hockey team. Ridder and her husband helped build the first women's-only college ice hockey facility, and which became the Ridder Arena, home to the Minnesota Golden Gophers women's ice hockey. The Ridders gifted $500,000 towards the project which opened in 2002, and remained the sole facility dedicated to college women's ice hockey until the Wisconsin Badgers opened LaBahn Arena in 2010. Robert Ridder died in 2000 before the arena's completion, but Kathleen Ridder attended the opening night and dropped the ceremonial first puck.
Publications
Ridder authored a total of seven books and articles, including three autobiographical books of her life: Books
Kathleen Incorporated.. Privately published, St. Paul Minnesota.
A Woman Ahead of her Time.. Privately published, St. Paul Minnesota.
Stories by Minnesota women in sports: leveling the playing field.. St. Cloud, Minnesota. North Star Press
Articles
Kathleen C. Ridder papers, 1978–1985. Minnesota Historical Society.
The Women's Institute and how it revived downtown St. Paul: speakers, style shows, and 12,000 shoppers.. Ramsey County history. Vol 32, no. 3.
A win at Wimbledon in 1959: links, courts, lanes, diamonds: Ramsey County's women athletes and their history of success.. Ramsey County history. Vol 33, no. 3.
Later life
Ridder was married to Robert for 56 years, until his death in 2000. She moved to Florida in 2008. She died at home in Lantana, Florida on April 3, 2017.
Honors and awards
Ridder was inducted into the University of Minnesota M Club Hall of Fame in 1990 as a benefactor, and received the Director's Award in 2004 in recognition of her generosity and service to the Minnesota Golden Gophers sports programs. The American Hockey Coaches Association recognized Ridder and her late husband in 2009 with the Joe Burke Award, for dedication to women's ice hockey.