It Happened In Hillsborough: The Blackwell’s Mill and Dam

Beginning with the removal of the Calco Dam on the Raritan River in 2011, the New Jersey Department
of Environmental Protection has been overseeing a project to open the waterways of the Raritan and
Millstone Rivers to migratory fish. Other dam removals have included the Robert Street (2012) and
Nevius Street (2013) dams on the Raritan and the Weston Mill Dam (2017) on the Millstone. The success
of the latter project allowed American shad to spawn in the Millstone River for the first time in 173
years. Now the NJDEP has turned its attention to the Blackwell’s Mill dam.

The Blackwell’s Mill and Dam

Peter Schenck built the first mill on the site in 1746, about the same time the first bridge was
constructed across the Millstone River into Franklin Township. Schenck was a wealthy landowner who,
at his death in 1780, left 2,400 acres of property in New York state, as well as the Millstone River mill
and at least one other mill in Hillsborough at Rock Mill in the Sourlands. The mills passed to his son-in-
law, Archibald Mercer, who had experience operating other mills in New Brunswick and Bound Brook. 
The original mill burned down in 1806, and by the time it was rebuilt a few years later, ownership had
passed to an uncle of William Blackwell, and by mid-century, William himself, thereby gaining the name
by which we know the village today. William Blackwell owned the mill until 1864 and was succeeded by
his son, John, until 1871.

A fire on the evening of April 26, 1905, completely destroyed the mill, which had recently been
equipped with new machinery and was then valued at $12,000 (more than $350,000 today). The
property, along with three houses and 17 acres of land, was scheduled to be sold at auction on July 7,
1905, but the auction was halted when bids fell well below the appraised value.

The planned removal of the five-foot-high concrete dam at the mill site will not only reintroduce
migratory fish such as American shad and blueback herring to the upper reaches of the Millstone but
also provide kayakers and canoers with unimpeded recreational opportunities between Kingston and
Manville.

The dam abutments and remnants of the mill, which can still be observed at times, will remain as part of
historic preservation efforts.
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Gregory Gillette has been writing about local history for 20 years, starting with his Courier News column
“Gillette on Hillsborough” and continuing today with a Facebook page of the same name. He was named
as Hillsborough’s first Local Historian in 2025.