The Rockwood Woolen Mill was established in 1867 by brothers John Richard, Thomas, and Joseph Harris, and their brother-in-law Thomas Wetherald. The firm advertised in publications in nearby cities such as Guelph, Milton, and Georgetown. The business thrived. Over the years, the mill was powered by the water of the Eramosa River, hydro, and steam.
In the 1880s, a fire harshly damaged the mill. It was replaced by a stone structure in 1884. One of the founding brothers, John Richard Harris, died in 1899; as a result, his sons took over the business. During the First World War, the mill would frequently operate 24 hours a day, securing vast orders for Canadian army blankets. The mill closed its doors in 1931, in the midst of the Great Depression
After the closure of the mill, William Harris, son of John Richard, transformed the site into a private park named Hi-Pot-Lo Park. In 1959 the Grand River Conservation Authority obtained the mill and land from Harris, and the official opening of the park took place in 1963.
A large restoration of the mill ruins was completed over the winter of 2010, allowing it to be open to the public for the 2011 season.
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