Gilbert Stanley Underwood (June 5, 1890 – August 3, 1961) was an American architect best known for his National Park lodges.

After opening an office in Los Angeles that year, he became associated with Daniel Ray Hull, a landscape architect, of the National Park Service.

His surviving Utah Parks Company buildings are considered exceptional examples of the Rustic style of architecture, and are all listed on the National Register of Historic Places.

While working for the federal government, Underwood produced the preliminary designs for the Timberline Lodge, Mount Hood, Oregon, and went on to design more than 20 post offices, two major federal buildings, and the U.S. State Department Building.

Following retirement but utilizing an association with John D. Rockefeller Jr., and the Williamsburg Lodge project in Virginia, Underwood designed as his last major commission the Jackson Lake Lodge (1950–1954), Grand Teton National Park, Wyoming.