John Altham (1589 – November 5, 1640) was a British Jesuit missionary who came to North America to preach to the Native Americans.
He was born in Warwickshire, England, in 1589. He was one of the two Jesuits who accompanied Cecil Calvert, 2nd Baron Baltimore in 1633 and arrived in the Chesapeake Bay in 1634. Upon landing, he obtained a hut from its Indian owner, which he fitted up for religious service, and it was afterward known as "the first chapel in Maryland." He performed his missionary work among the Indians around Kent Island from 1634 till his death from yellow fever, in nearby St. Mary's, Maryland, in 1640.