24/7 Trauma and Biohazard Cleanup in Byrnes Mill, MO

Byrnes Mill, in northern Jefferson County, takes its name from a grist mill on the Big River purchased in 1865 by Patrick C. Byrne, an Irish immigrant who arrived in America in 1849 and assembled an 800-acre estate.

The Byrne family held the mill property for more than 140 years, not selling the mill and most of the land until 2008.

Byrnes Mill was not incorporated until 1986, making it the youngest incorporated city in Jefferson County.

The ruins of the old mill and its dam still stand on the Big River, and the mill site is now an 18-acre city park with fishing access, a hiking trail along the river, a rentable pavilion, and the Hagemeister House, an 1871 cabin relocated to the park.

Byrnes Mill had 3,173 residents at the 2020 census, up from 2,781 in 2010 and just 1,578 in 1990 — the population has doubled since incorporation as St. Louis commuters moved outward.

At the 2010 census, Byrnes Mill's 2,781 residents lived in 1,038 households, most of them families drawn by the semi-rural setting along Highway 30.

The Big River, a tributary of the Meramec River, forms Byrnes Mill's western boundary, while Missouri Highway 30 forms most of its eastern border.

The city covers 5.26 square miles, of which about 0.12 square miles is water, including Lake Montowese.

German is the most commonly reported ancestry in Byrnes Mill, claimed by over 40% of residents in census data.