US Post Office is located at 1120 North Ave, Plainfield, NJ. This business specializes in Post Offices. US Post Office is open Mon, 8am-4:05pm ; Tue, 8am-4:05pm ; Wed, 8am-4:05pm ; Thu, 8am-4:05pm ; Fri, 8am-4:05pm ; Sat, 8am-12:05pm ; Sun, Closed. and accepts American Express, Discover and Visa.