William Neil was born around 1746 in Belfast, Northern Ireland, and graduated from Glasgow College in Scotland. When he returned to Belfast, he became an important and large-scale manufacturer of linen. He and his wife, Margaret, had seven children: Thomas, Charles, Robert, Ann, Elizabeth, Sarah, and Margaret. Around 1790, William, Margaret, and several of the children emigrated to America and settled in Portsmouth, New Hampshire. There, William and Thomas operated a store specializing in linens and tea, located on Buck Street. William's son, Charles, who remained in Belfast, assisted in coordinating trans-Atlantic trading.
Around 1798, Ann Neil married merchant George Andrews of Dover, New Hampshire, cementing the business relationship between Andrews and her father. Thomas Neil (c. 1773-1850) married Sarah McNeil (c. 1772-1821), and they had one son, Thomas, who died at sea in 1820. William Neil died in 1825, aged 79, and after his death, Thomas carried on the trade.