Very little is known about Mayflower passenger John Allerton. It is generally assumed that he was related in some way to well-known Mayflower passenger Isaac Allerton: perhaps a brother. If that is the case, then he may also hail from the vicinity of Ipswich, co. Suffolk, England. He appears to have been living in Leiden, Holland, with the Pilgrim congregation established there. He buried a child at St. Peters in Leiden on 21 May 1616, and at that time he resided in the same neighborhood as Isaac Allerton.
Governor William Bradford, writing in 1651, informs us that John Allerton intended to return to Leiden to help others in the church prepare for their voyages over, but his death the first winter at Plymouth prevented those plans from being fulfilled.