Portland Observatory | |
 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.