The Gen. Mason J. Young House, also known as the William Boyd House, is a historic house and connected farm complex at 4 Young Road in Londonderry, New Hampshire. The main house is reported by family accounts to have been built in 1802, on a farm that was in active use since 1757. It is a 2-1/2 story wood frame structure with a gable roof and a central chimney. It is five bays wide and three deep with a columned portico (c. 1900) sheltering its front entry, and a single-story porch (dating to the mid-19th century) extending along the side. The interior has well-preserved period woodwork. A two-story wing extends to the rear of the house, which is further extended by a series of sheds connecting the house to a carriage house and dairy barn.