Mary Allerton was born in Leiden, her parents were Isaac and Mary Allerton who were Separatist passengers on the Mayflower.

Around 1636, she married Thomas Cushman, who had come to Plymouth in 1621 at the age of thirteen on the ship Fortune with father Robert Cushman, a prominent member of the Pilgrims' congregation in Leiden. Thomas and Mary had a surprisingly prosperous family; seven of their eight children survived to adulthood, got married, and provided at least 50 grandchildren. Thomas and Mary both lived to an old age, especially considering the medical assistance available in the 17th century, having never moved from Plymouth.

Mary Allerton Cushman was a settler of Plymouth Colony in what is now Massachusetts. She was the last surviving passenger of the Mayflower.  She arrived at Plymouth on the Mayflower when she was about four years old and lived there the rest of her life and died aged 83.