Boyd's Windmill, also known as Boyd's Wind Grist Mill, is a historic smock mill at Paradise Valley Park on Prospect Avenue in Middletown, Rhode Island. John Peterson built the windmill on Old Mill Lane in Portsmouth, Rhode Island in 1810, and William Boyd purchased it in 1815. It originally had four common sails, but four more were added by the family. The mill is a timber-frame structure, octagonal in shape, and about 30 feet (9.1 m) tall, with a rotating cap powered by eight vanes with canvas sheets. The grindstones in the middle of the mill are Fall River granite; the upper one, which is connected to the power mechanisms, rotates six times for each turn of the mill's main shaft. In 1916 Benjamin Boyd removed the original vanes and powered the mill using a gasoline engine. It is one of only two historic windmills (out of what was estimated to be more than thirty) to survive on Aquidneck Island.