US Post Office is located at 14 Clinton Ave, Plainfield, NJ. This business specializes in Post Offices. US Post Office is open Mon, 9am-4pm; Tue, 9am-4pm; Wed, 9am-4pm; Thu, 9am-4pm; Fri, 9am-4pm; Sat, 8:05am-12pm; Sun, Closed and accepts American Express, Discover, Mastercard and Visa.