Son of
Donald E. Wahlberg Sr. and
Alma McPeck. His father was of half Swedish and half Irish descent, and his mother's ancestry is 11/16ths Irish, one eighth French-Canadian, one eighth English, and one sixteenth Scottish. Robert's paternal grandfather, Axel Simon Wahlberg, was the son of Swedish immigrants, Axel Gustaf Wahlberg and Ida Albertina Nordstrom.