Portland Observatory

	Portland Observatory
	U.S. National Register of Historic Places
	U.S. National Historic Landmark
	The Portland Observatory in 2024
Location	138 Congress St; Portland, Maine
Coordinates	43°39′55″N 70°14′54″W / 43.66528°N 70.24833°W
Area	less than one acre
Built	1807
NRHP reference No.	73000122
Significant dates
Added to NRHP	April 24, 1973
Designated NHL	February 17, 2006

The Portland Observatory is a historic maritime signal tower at 138 Congress Street in the Munjoy Hill section of Portland, Maine. Built in 1807, it is the only known surviving tower of its type in the United States. Using both a telescope and signal flags, two-way communication between ship and shore was possible several hours before an incoming vessel reached the docks. The tower was designated a National Historic Landmark and a National Historic Civil Engineering Landmark in 2006; it is now managed by Greater Portland Landmarks, a local historic preservation nonprofit. It is open to the public as a museum.