He was in private practice in Pottstown from 1961 to 1981. During that time, Yohn served as an assistant district attorney (1962–1965) and as a member of the Pennsylvania House of Representatives from 1968 to 1980. In 1981 he was elected as a judge on the court of common pleas for Montgomery County, a position he held until 1991.
From 1961 to 1981, Yohn operated his private practice in Pottstown. He served as an assistant district attorney from 1962 to 1965 and was a member of the Pennsylvania House of Representatives from 1968 to 1980. In 1981, he was elected judge on the court of common pleas for Montgomery County, a position he held until 1991.