On July 19, 1770, Dickinson married Mary Norris, known as Polly, a prominent and well educated thirty-year-old woman in Philadelphia with a substantial holding of real estate and personal property (including a 1500 volume library, one of the largest in the colonies at the time) who had been operating her family's estate, Fair Hill, for a number of years by herself or with her sister. She was the daughter of a wealthy Philadelphia Quaker, and Speaker of the Pennsylvania General Assembly, Isaac Norris and Sarah Logan, the daughter of James Logan, both deceased. She was also cousin to the Quaker poet Hannah Griffitts. Dickinson and Norris had five children, but only two survived to adulthood: Sarah Norris "Sally" Dickinson and Maria Mary Dickinson. Dickinson never formally joined the Quaker Meeting, because, as he explained, he believed in the "lawfulness of defensive war". He and Norris were married in a civil ceremony.