The Machias Post Office and Customhouse is located at the western corner of Center Street and Main Street (United States Route 1) in the heart of Machias' downtown area.

It is a two-story red brick building, topped by a hip roof and set on a granite foundation.

One principal entrance is on the first floor of that section, set in a round-arch opening with keystone and pilastered columns.

The Center Street facade is five bays wide, with a similar arrangement and styling of doors and windows.

[2] Early federal government facilities in Machias were located in leased spaces secured by the postmasters and customs collectors, a condition eventually found inadequate due to frequently changing addresses, and spaces that were not properly configured for the purpose.