McKillip, who served with the Army Air Corps in World War II and later was a high school football coach, arrived at St. Mary's in 1970 and helped broaden the scope of the school's athletic program.
During McKillip's tenure as AD, St. Mary's men's basketball team tied for first in the West Coast Athletic Conference in 1980 and won a West Coast Conference title and earned an NCAA Tournament berth in 1989; the school also won NAIA national championships in women's soccer (1984) and women's volleyball (1986).
McKillip helped launch St. Mary's Athletic Summer Camp program in 1970, laying the foundation for a program that grew from 200 youngsters in its inaugural year to 2,500 last year.
He was enshrined into St. Mary's Athletic Hall of Fame in 1997.
Dick Callahan, longtime St. Mary's football public address announcer, was hired by McKillip in 1975.
"Don really enhanced the athletic department," Callahan said. "He had a vision beyond what you might think of him if you just talked to him. He cared about his employees, and he cared about the college."
McKillip is survived by his wife, Eunice; his sister, Marion Farrell; his brother, Leo; his children, Don, Sandra and Michael; nine grandchildren and nine great-grandchildren.
Visitation will be from 5-9 p.m. Thursday at Hull's Walnut Creek Chapel. A Mass celebrating his life will be said at 10 a.m. Friday at St. Anne Catholic church at 1600 Rossmoor Parkway.