US Post Office is located at 250 Main St, Cambridge, MA. This location is in the Kendall Square neighborhood. This business specializes in Post Offices. US Post Office is open Mon, 9am-4:05pm; Tue, 9am-4:05pm; Wed, 9am-4:05pm; Thu, 9am-4:05pm; Fri, 9am-4:05pm; Sat, Closed; Sun, Closed and accepts American Express, Discover, Mastercard and Visa.