William Tailer was born in Dorchester, Massachusetts Bay Colony on February 25, 1675/6 to William Tailer and Rebecca Stoughton Tailer. His mother was the daughter of early Massachusetts settler Israel Stoughton and sister to magistrate William Stoughton. His father was a wealthy landowner and merchant. His father owned commercial real estate in Boston and was a member of the Atherton Company, one of New England's most powerful and well-connected land development partnerships. He was also one of "a selected fraternity" of merchants engaged in the "eastward trade" with neighboring French Acadia, one of whose leading members was Boston merchant John Nelson. Tailer's father committed suicide in 1682, apparently suffering from depression which may have been brought on by financial reverses.