The Rev. John Gemmill was the son of John Gemmill Sr. a trustee of the great Valley Presbyterian Church and a Scottish immigrant from Kilmarnack. He immigrated to Philadelphia in 1781, and the next year, entered the University of Pennsylvania where he afterwards graduated and became an instructor. He was conferred an AB degree in 1785, and an AM in 1788 and then studied theology and ordained a Presbyterian minister in 1790. He preached in the Great Valley, Chester County, 1790-1795, and was offered (and accepted) one of the best Congregational pulpits in New England at New Haven. Later he was offered the Chair of Divinity in Yale College by President Dwight, but declined the Honor. He first married Sarah Knox in Philadelphia, the widow of Colonel Robert Knox of the Continental Army who died one year after marriage. In October, 1803, he married his second cousin Rebecca Irwin. He died in West Chester on Dec. 14, 1814, at the close of his single term in the Senate.