The Old Walnut Ridge Post Office is a historic commercial building at 225 West Main Street in Walnut Ridge, Arkansas. It is a 1-1/2 story T-shaped brick structure, five bays wide, with a side gable roof and a full concrete basement. Its Colonial Revival features include a centered entry, flanked by Ionic pilasters and topped by a broken gabled pediment. The remaining bays are filled with nine-over-nine sash windows.