US Post Office is located at 311 Oak Grove Ave, South Beloit, IL. This business specializes in Post Offices. US Post Office is open Mon, 8:05am-5pm; Tue, 8:05am-5pm; Wed, 8:05am-5pm; Thu, 8:05am-5pm; Fri, 8:05am-5pm; Sat, 8:05am-12pm; Sun, Closed and accepts American Express, Discover, Mastercard and Visa.