In April 1893 Thomas Anwyl petitioned the Louisa County Board of Supervisors for construction of a permanent bridge over Long Creek on the Louisa-Washington county line. Immediately after it approved Anwyl's request, the board opened bidding for a new iron bridge at this location. A contract to supply the truss superstructure for this crossing--and for Gipple's Quarry Bridge over Buffington Creek in Elm Grove Township--was awarded to the Gillette-Herzog Manufacturing Company of Minneapolis, Minnesota, for a total cost of $1,174 for both. The latter structure was to be placed on traditional stone masonry abutments and piers; the County Line Bridge, on the other hand, was to be supported by patented cast iron columns, manufactured by the Cast Iron Pile and Bridge Company of Keosauqua, Iowa. Using steel components rolled in Pittsburgh by Carnegie, Gillette-Herzog fabricated the medium-span pony trusses and erected them by September 1893. Both spans have since carried county-road traffic in essentially unaltered condition. With its pin-connected detailing and Pratt design, the pony truss on the County Line Bridge typifies iron bridge construction in Iowa from the early 1890s. What distinguishes this structure from most of its peers is its unusual lower chord configuration, with the end panels sloped downward from the bearing shoes to the center panels. Only a handful of spans employing this Pratt truss variation has been identified by the historic bridge inventory. The bridge is further distinguished by its unique substructure, manufactured by a small-scale Iowa enterprise. Operating briefly in the 1890s, the Cast Iron Pile and Bridge Company evidently supplied bridge components to counties in southern Iowa and northern Missouri. The Keosauqua firm was never a major player, however, and the cast iron piers on the County Line Bridge represent the only known remnant of the firm's work. The County Line Bridge is thus technologically significant as a well-preserved, early example of wagon bridge construction in Iowa, an uncommon Pratt variant and as the last resource remaining from this in-state bridge builder [adapted from Fraser 1991].