The Newcastle Main Post Office is a historic post office building in Newcastle, Wyoming. Built in 1932, it was constructed as part of a facilities improvement program by the United States Post Office Department. The post office in Newcastle was nominated to the National Register of Historic Places as part of a thematic study comprising twelve Wyoming post offices built to standardized USPO plans in the early twentieth century.

• Photographs of the Newcastle Post Office at the National Park Service's NRHP database
• Newcastle Main Post Office at the Wyoming State Historic Preservation Office
• United States Post Office (Newcastle, Wyoming) at the National Archives and Records Administration