Mercer County Bridge No. 1801 is on the National Register of Historic Places. This is Mercer County's only remaining covered bridge. The bridge is located on Township Road 471, approximately one half-mile east of S.R. 18, in Pymatuning Township, Mercer County, Pennsylvania. The bridge is situated in a rural area and spans the Shenango River.
The single-lane Mercer County Bridge 1801 consists of a single span, Smith Truss covered bridge on sandstone ashlars. The structure has a span of 122'-6" backwall to backwall on a 90 degree skew. The roadway is 16'-7" between the trusses. The bridge is 118'-7" center to center of bearings. Two inch timber planking is laid diagonally over the floorbeams. Two inch timber planking is laid longitudinally for wheel paths, and these are nailed to the main flooring. The 2" x 12" floorbeams are spaced at 1'-9" and are notched to rest on the lower chords.
The timber truss diagonals are hand hewn timbers of various sizes. The upper chords are bolted 6" x 10" and the lower chords are bolted 6" x 12" timbers. These have spacer blocks to permit the diagonals to pass through forming a mortise and tenon connection.
The structure was constructed in 1868 by the Smith Bridge Company of Tipp City, Ohio. Devised and patented in 1867 by Robert Smith, both tension and compression members were all wood. During the period of 1867 to 1870, Smith built 15 of these patented structures in Miami County, Ohio.
Smith usually assembled the trusses in his home yard and shipped them by rail to the destination. Standard charges for a complete bridge put up by Smith's company was $18 per foot for a bridge span of 125 feet.
The Kidds Mill bridge is the only one of Smith's patented bridges still standing east of Ohio.