The Masontown Bridge is a four-lane, concrete, plate girder bridge that carries vehicular traffic across the Monongahela River between Masontown, Pennsylvania and Monongahela Township, Pennsylvania (near Carmichaels), by way of Pennsylvania Route 21.

The current structure was completed and opened in December 2015 after a three-year project costing $49.6 million to replace the previous truss bridge that was built in 1925 and rehabilitated in 1993.

[3] The Pennsylvania Department of Transportation undertook the bridge replacement project as part of a years-long effort to modernize and improve Route 21 and expand it in some areas.

[5] The structure passed directly in front of the Hatfield's Ferry Power Station and carried a large amount of associated truck traffic.

It replaced a ferry at the site that had been established in 1769.