Find a USPS Mailbox Near You in ROCKLAND, MA. Name: Rockland Post Office; Address: 39 Webster Street, Rockland, Massachusetts, ; Phone: ; Hours: Monday:: am - pm, Tuesday. US Post Office is located at 39 Webster St, Rockland, MA. This business specializes in Post Offices. US Post Office is open Mon, am-5pm; Tue, 8:05am-5pm;.