I first began flying in the early 70's, when I began to attend college in Oshkosh, Wisconsin. The airline of choice (i.e. the only one available) was the 'Ruptured Goose', aka North Central Airlines. While my memories of the flights are vague (hey, I was a child of the 70's-- in Wisconsin), I do remember the airport being a smaller version of a bus station located in a hanger.
At some point, I even think they had direct service to LGA, but the details are 'hazy'.