US Post Office is located at 39 Main St, Greenwich, NY. This business specializes in Post Offices. US Post Office is open Mon, 8am-4:59pm; Tue, 8am-4:59pm; Wed, 8am-4:59pm; Thu, 8am-4:59pm; Fri, 8am-4:59pm; Sat, 9am-12pm; Sun, Closed and accepts American Express, Discover, Mastercard and Visa.