William Seawright was born ca. 1720, near the city of Londonderry, in the north of Ireland. He emigrated from Ulster, Ireland, ca. 1738 and settled in Lancaster County, Pennsylvania. He and his wife, Anne Hamilton, had five children. He died in 1771 in Lampiter Township, Lancaster County, Pennsylvania. Descendants lived in Pennsylvania, Indiana, Ohio, and elsewhere. Some descendants spell their name "Searight.".