Active in running Advent:Publishers, he created covers for many of their books.
Stopa met Joni Cornell (nee Doyle) at Pittcon and the following year traveled out to Seattle with a group of fans, including Joni, for Seacon. By 1962, they were married and living at Stopa’s family sky lodge in Wilmot, Wisconsin, where they began hosting Wilcon, a three-day long invitation-only relaxacon, in 1963.
Throughout the 1960s, the Stopas entered and won many costume contests. Jon was responsible for publications at Chicon III and his picture, in costume appeared in The Proceedings: Chicon III. In the early 1970s the couple helped found ISFiC. He was part of the Chicago: 1959 Worldcon bid.