William Underhill was born 26 November 1751 in Greenville, Greene County, New York, USA to William Underhill (1727-1784) and Mary Dean (1728-1778) and died 24 September 1817 Tuckahoe, Westchester County, New York, USA of unspecified causes. He married Dorshia Taylor (1749-1842) 1769 in New York, United States.
Children
| Name | Birth | Death | Joined with |
| William Underhill (1769-) | |||
| Noah Underhill (1770-1808) | |||
| Jane Underhill (1774-1852) | |||
| Nathaniel Underhill (1774-1855) | |||
| Gilbert Underhill (1775-1867) | |||
| Sarah Underhill (1781-) | |||
| Benjamin Taylor Underhill (1785-) | |||
| Charlotte Underhill (1787-1848) | 21 March 1787 Westchester County, New York, USA | 11 December 1848 Greenville, Westchester County, New York, USA | William Wright (1777-1852) |
| Mary Underhill (1789-) | |||
Siblings
| Name | Birth | Death | Joined with |
| Helenor Underhill (1750-1840) | |||
| William Underhill (1751-1817) | 26 November 1751 Greenville, Greene County, New York, USA | 24 September 1817 Tuckahoe, Westchester County, New York, USA | Dorshia Taylor (1749-1842) |
| Johnathan Underhill (1752-1796) | |||
| Elizabeth Underhill (1755-1843) | |||
| Ann Underhill (1756-1776) | |||
| Margaret Underhill (1758-) | |||
| Gilbert Underhill (1763-1843) | |||
| Deborah Underhill (1767-1848) | |||