Caption reads "Another View of No. 3 Mill Looking down the lumber conveyor from sorting table. The seven cabins house the electric motors that drive the conveyor. Each drives twenty nine rolss. Lumber moving at the rate of three and a half feet a second takes nearly five minutes to reach the sorting table."
Mill No. 4 was built in 1892, just 300 yards East of Mill No. 3 on the shore of the Ottawa River. Like Mill No. 3, it was steam-operated and equipped with the latest technology of its day. Mill No. 4 had a a 125-foot high "Iron Bottle" burner. It was the last mill built by the McLachlin Bros. Due to an economic downturn in the 1920s, only Mills 3 and 4 were still in operation by 1923. They ceased operation in 1929, and Mill No. 4 was finally demolished in 1936.
Constructed in 1867, Mill No. 2 was the second mill built by Daniel McLachlin on the Madawaska river at the bridge. Called "The Little Mill", it was smaller in size and output than Mill No.1, beside it. After the much larger Mills No. 3 and 4 were built along the shore of Chats Lake in the 1870s and 80s, Mills no. 1 and 2 slowly ceased production. All of the mills ceased operation in 1929 due to a decline in business over the 1920s. However, Mill No.2 operated again to saw logs for shipment to the J.R. Booth Company from 1936 to 1938. Its stone foundations were demolished in 1972 when Ontario Hydro constructed the weir.
Mill no. 1, known as "the big water mill," was built in 1865 by Daniel McLachlin on the East bank of the Madawaska river. This was not McLachlin's very first mill, however. In the 1850s, McLachlin was operating a mill he refurbished from the remnants of a previous mill built by the Buchanan brothers in 1833. It was water-powered and had a single saw which turned out one board at a time. When the Brockville & Ottawa railway was built to Arnprior in 1865, the new mill was constructed on the same site to produce much more lumber for transport to new markets.
With the building of the newer steam-saw Mills 3 and 4 in subsequent decades, the equipment in Mill No.1 slowly became outdated. In 1892, with Mill No.4 having just been built, it was deemed expedient to discontinue the work in Mill No.1. By 1905, the insurance plan for the McLachlin Bros. Sawmills & Lumber Yards lists Mill No.1 as a "late mill" repurposed as a storehouse.
The steam-powered No. 3 Mill was built in 1871 along the southern shore of the Ottawa river, east of the Madawaska. It burnt in 1875 and a new mill was built on the same site, opening for production in 1882. It was equipped with the newest machinery of the day, including a 190 foot "Iron Bullet Waste Burner." With the construction of Mills 3 and 4, output grew immensely and the McLachlin Bros. were producing 60,000,000 feet of lumber in a good year. A newspaper article from 1923 stated that there was a downturn in business and that only Mill 3 and 4 were in use for a few months per year. The mills ceased operation in 1929. Its demolition date is unknown.