William J. Munn was one of the Munn Brothers.
Excerpted from an article on the Fowler Block by Philip Gallos.
On the ground floor of the building, these two Munns, with their brother Albert, opened the Munn Brothers' Grocery. It was a large and successful business — so much so that most older residents call 76 Main Street the "Munn Block".
The Munns’ was the first grocery in the village to have walk-in coolers, and they had a fleet of three delivery trucks.