Built to replace the previous federal building, which had been destroyed by fire, the Sitka Post Office and Courthouse is a Moderne, concrete structure. Designed by Gilbert Stanley Underwood, the building was constructed by J. B. Warrack Company for $155,888. The main block of the building is five bays long and rises two stories above a raised basement. The first- and second-floor windows are joined vertically by slightly recessed, ornamented spandrels. A shallow belt course across the tops of the second-story windows and flat circles framing the lettering across the top of the building constitute the only other ornament on the facade. The roof is flat and there is no cornice. At either end of the main block are one-story wings, one bay wide. On the interior, the post office lobby on the first floor has quarry tile flooring and wainscoting. At present, the post office has moved out and the building's future is uncertain.
Concrete construction was introduced to Alaska at the Sheldon Jackson Museum, located at the other end of Lincoln Street. It reached its culmination in this building, a sleek, modern structure that makes the most of its flat surfaces by presenting a pure form.