The Observer Building is a historic commercial and residential building at 128 Union Square in Dover-Foxcroft, Maine. Built in 1854, it is an architecturally unusual Greek Revival wood-frame "flatiron" triangular building with a variable-pitch gable roof. In addition to its architectural significance, it is also historically significant as the home for many years of The Piscataquis Observer, one of Maine's oldest weekly newspapers. The building is now owned by the Dover-Foxcroft Historical Society, which uses it as a museum and storage space. It was listed on the National Register of Historic Places in 1998.