The Dennington Bridge, a long single-track timber-beam rail bridge built as an important component of the Warrnambool-Koroit section of the Terang-Port Fairy Railway in 1890, is historically, scientifically and aesthetically significant at State level.
Completion of the Warrnambool-Port Fairy sections of the east-west railway in 1890 allowed the rapid transport of fresh fish and crayfish across the Denningron Bridge towards Melbourne and Geelong markets, and made the transport of potatoes and onions from the Koroit area to metropolitan markets more easy and efficient than it had been with the previous process of road haulage to coastal steamers. The Victorian Railways would henceforth provide real competition to the shipping of Warrnambool, Belfast and Portland, that had provided the far Western District's previous main freight links with Melbourne and the wider world. Whereas the main road networks of the district had long run north-south to link with coastal ports, there was for the first time a quick and servicable west-east overland transport system connecting with Victoria's population concentrations. The big timber bridge over the Merri River at Dennington was one vital link in this new transport order for Victoria's western borderlands. The section of the Geelong-Port Fairy line between Warrnambool and Koroit for which the Dennington Railway Bridge was created, was also understood within the region as a key link-section providing access to a wide ranging network of western Victorian railways linked up through such major railway junction points as Koroit, Hamilton, Horsham and Ararat. It was built in conjunction with the adjoining Koroit-Hamilton Railway, which project created strong and often bitter political controversy between inland junction towns like Hamilton, Dunkeld and Koroit on the one hand, and between rival regional ports like Portland, Port Fairy and Warrnambool on the other. In this regional mercantile rivalry, the section of line containing Dennington Bridge elevated the interests of Warrnambool's port over against those of Portland and Port Fairy, by providing possible direct access for north-western agricultural and pastoral produce carried by several railways that converged at junction points near Hamilton.
Scientifically, the Dennington Bridge is Victoria's best surviving example of a large timber-beam rail bridge with an extensive and intact system of stay-piles on either side of its main river-channel section. With its 41 spans it is the fourth-largest surviving rail bridge built to the standard Victorian Railways fifteen-feet (4.6 metre) timber-beam-span design. Aesthetically, the Dennington Bridge has long made an important contribution to the local landscape. Its long and low timber profile fits well into a context of rolling Western District farmland, and (unlike most other big timber rail bridges) this attractive timber profile stands out clearly from a number of vantage points.