Mattson was elected State Auditor at the age of 26, the second-youngest to attain statewide office in Minnesota; the distinction of being the youngest goes to Jim Lord, who was 25 when elected State Treasurer.
Mattson and his wife, Marge, are the parents of two daughters, Kimberly and Jennifer. Kimberly operates Kimberly Boutique stores in West Hartford and Guilford, Connecticut, and Jennifer is an attorney in Saint Paul.