[1] The Portland Main Post Office is located on the east side of Forest Avenue, across the street from Deering Oaks park.

The southern part of the building is its older portion; it is a steel-framed structure finished in brick and stone, two stories in height.

The addition to the north is of roughly equal size to the original, but has much simpler styling.

When built, it was the second largest post office in New England, second in size to that in Boston, Massachusetts.

The addition, built in 1967 to house other federal offices, was designed by Richard Wright of Lewiston.