John Jay Phelps was born in Paris, in 1861 to a wealthy Sheffield family. A Yale graduate, he thrived in yachting and built his yacht, Brunnhilde shortly after graduating. He sailed the Brunnhilde around the world, it is rumored that this is the first trip by an American yacht. Shortly after his return in 1888 he married Rose Hutchinson and had two daughters. It was after the birth of his second daughter, when he purchased the 12-acre Rogers Island. Before the purchase, it had been used for quarrying and thus had few trees. In 1903, he began to build his mansion and renamed the island Yonkomis. The island was landscaped, vegetable and flower gardens were laid out, trees were planted, and bridle paths were planned. During the construction, he summered in a cottage nearby. When the mansion was finally complete, it was the largest house in Branford. No other property rivaled the 27 room Tudor with a tennis court, golf course, and guest cottage. During World War I, he built his own submarine chaser which was commissioned by the Navy with Phelps as the Commanding Officer.

Information obtained from Blackstone Library, Branford Connecticut