The 1874 McConnell's Mill Covered Bridge is a historic, wooden covered bridge located in Slippery Rock Township, Lawrence County, Pennsylvania. This bridge spans Slippery Rock Creek in McConnell's Mill State Park. This 96-foot-long bridge sits nestled in a gorge alongside a grist mill that dates back to the 1860s and a dam inside the park.

This historic bridge with a Howe truss built on stone foundations and supported by steel girders, is one of only four existing Howe trusses in Pennsylvania. Howe trusses combine a variation of a regular king-post truss with diagonal wooden members acting in compression and vertical iron rods acting in tension. There were variations on the truss, one of which added a second wooden diagonal to each panel. The McConnell's Mill Bridge employs this crossed-diagonal system. Its red-painted board-and-batten exterior gives the bridge the semblance of a barn over a river.

Lawrence County in Pennsylvania doesn't possess many covered bridges, though there is evidence that at least seventeen of them existed in the county at one time or another, only McConnell's Mill Covered Bridge and the Banks Covered Bridge still exist.

The only substantial alterations to the original bridge are a steel truss supporting the wooden deck and asphalt roofing paper that was attached to the roof beams in the late 1950s. In 1978, a bridge inspection undertaken by Frank B. Taylor Engineering Company of New Castle, Pennsylvania, reported the bridge in good condition overall, recommending only that bridge inspections be stepped up to every two years and that signage indicating a weight limit of five tons and a clearance of 10'-0" be posted. The study also noted that the bridge was covered in graffiti dating back to 1905. Another study by the same company in 1995 recommended the replacement of the wooden decking and other rotted wooden components, the replacement of the roof, and a thorough re-painting. The bridge was extensively rehabilitated in 2016.

A bridge at this location would probably never have been built at all had not McConnell's Mill been there in the first place. Indeed, the story of the bridge was - and continues to be - linked to the mill that later gave its name not only to the bridge but also to the state park around it. The first gristmill on this site was built in 1852 and then rebuilt in 1868 after the first was destroyed by fire. Thomas McConnell bought the mill in 1875 and improved it by replacing the waterwheel with water turbines and the grinding stones with cylindrical roller mills. As one of the first roller mills in the country, it processed corn, oats, wheat, and buckwheat for local customers. The mill operated until 1928, was conveyed to the Western Pennsylvania Conservancy in 1946 and officially became McConnell’s Mill State Park in October of 1957. Since then, the mill was transformed into a museum in the 1960s.

In 1980, the bridge was recognized for its historical significance by being placed on the National Register of Historic Places, along with the Banks Bridge.

Located at: N40 57.18    W80 10.22     -     WGCB #38-37-01

Photographed in May 2023.