Owner Sherman Hines has traced the construction back to 1699, built by the French as a mission and a fortification against the English after searching old maps and books.
"As far as I can find in any research I have done, it is the oldest building east of Quebec City," he said.
Hines, a photographer, bought the house in 1982 for $15,000 and a restoration was 30 years in the making.
"We drove up and I crawled around in this basement, it was full of mud and debris. I was doing kind of a duck walk around, I couldn't stand up, and I fell in love with it," Hines said.
Maps describe a building matching this description at the place where the St. Croix River meets the Avon.
"The light went off that it was a fortified church," he said.
Hines has restored the house to its former condition with as much period furniture as possible.
"Part of my fun is saving the buildings, the other part is finding the materials to fix them up with," Hines said.
The antique furniture, even some of Hines' trophies from big game hunting — it's all for sale.
Hines and his wife are downsizing.
"It was mainly a place for the children. It's a wonderful place for children to grow up, and now there are just two of us, and seven buildings, and we use three rooms," he said with a chuckle.
Hines says his first hope is that the house could become a museum. But if not that, it could be a winery or somebody else's home.
The asking price on the house is $2 million.