A landmark for pioneer architecture, the Old Stone Mill National Historic Site is a fine example of an early Georgian Industrial architectural style and is the second oldest building of its type in Ontario. A three-and-a-half-storey rectangular stone structure with classical proportions and a long façade, it was constructed by William Jones in 1810. Serving as the focal point for economic development in Delta in the early 19th century, the mill employed the most advanced mill technology of the time, using Oliver Evan’s book on automatic milling, published in 1795, as a guiding source for operations.

The back one-and-a-half-storey portion was added by Walter Denaut around 1860 to include turbines which were considered to be more efficient technology than the traditional water wheel. The windows are 12-over-8 throughout save those on the addition which are French-style. The adjacent horse shed had a second-storey room used as a courthouse, school, and meeting room. The Old Stone Mill spurred the development of a host of businesses in the Village of Delta, including a local distillery, which produced 15,000 gallons of whiskey and became the site of the first temperance sermon in Canada. It ceased operation in 1949 and the Delta Mill Society purchased it in 1961, extensively restored it and successfully recreated its original appearance. Today it provides remarkable historic milling demonstrations as well as a museum.