Rochester is said to have been born on 1 April 1647. The only source for this date is John Gadbury's Ephemeris, or a Diary for 1695 that gives the poet's birth date as ‘1o April ’ and the place as Ditchley. As Gadbury had been publishing his Ephemerides every year since 1655 and did not include the poet's birth date before 1695, this source can have little authority. A child born at Ditchley should have been christened in the parish church at Spelsbury, but Rochester's christening does not appear in the parish record. For lack of better evidence Gadbury's date must stand. Certainly when Rochester first attended the House of Lords on 10 October 1667, having been summoned by a special writ on 29 July, he was understood to be ‘in the twenty-first year of his age’.

At the time of the poet's birth Ditchley Park was in the possession of the poet's mother, Anne, Baroness Wilmot, as the guardian of the infant proprietor, Sir Henry Lee, her first son by her first marriage. After the death of Sir Edward Henry Lee in 1639, several suitors had been proposed for the 25-year-old widow only to lose their lives in the fighting. In September 1643 it became known that she was to marry the royalist general, Henry Wilmot. Wilmot, scion of an Oxfordshire family, had inherited the titles and the Irish estates of his father in May of that year, and was created Baron Wilmot of Adderbury in June 1643 for his services to the King at the battle of Roundway Down. He had been married for some months before, in mid-1644, he was found to be involved in a conspiracy to persuade Charles I to abdicate in favour of his son who, it was thought, would be more amenable than his father to the parliamentarians’ demands. Anne Wilmot was one of the St John family of Lydiard Tregoze, influential supporters of both the Crown and the rights of Parliament, who would be deeply implicated in the coming struggle for a Protestant succession and limitation of the power of the monarch. It was the consolidation of the ranks of such presbyterian gentry during the ineffectual reign of ‘Tumbledown Dick’ Cromwell that made the Restoration possible.