Grayson was born in 1736 to Benjamin and Susannah (Monroe) Grayson at Belle Aire Plantation. in what is now
Woodbridge, Virginia. His father had emigrated from Scotland to the confluence of the
Potomac River and
Quantico Creek which became
Dumfries, Virginia. Benjamin Grayson Sr. became a successful merchant and planter, as well as militia officer and (by 1731) one of the justices of the peace (who jointly governed the vast county of that day, in addition to their judicial duties). Their mother, twice-widowed, had been born to an important family upriver in
Westmoreland County and had children by her previous marriages to Charles Tyler and William Linton (also a Scottish-born merchant). One of her nephews,
James Monroe, would later serve in the Continental Army, succeed this man as U.S. Senator from Virginia and became President of the United States. Susanna Grayson bore three sons (Spence, Benjamin Jr. and William) and a daughter (also Susanna) in this marriage before she died in 1752, when this boy was ten. His father remarried, to another widow, Sarah Ball Ewell, who also had children by prior marriage, but none in this marriage before her husband died in 1757. William was sixteen when his father died, so his eldest brother (Benjamin Grayson Jr.) became his legal guardian until he reached 21 years. Benjamin Grayson Jr. and Spence Grayson, being the elder brothers, inherited their father's business and plantations approximating 2,800 acres in Prince William County, by a will drafted in 1753 which was admitted to probate in 1758 but no longer exists. However, William was well-provided for from the personal estate (which required a 10,000 bond), especially compared to his future commander, George Washington (whose far smaller inheritance caused him to earn a living by surveying beginning as a teenager). One of the Grayson plantations included a house on a hill above Dumfries that became known as "Grayson's Hill" and later "Battery Hill" (for a Confederate battery during the American Civil War). The other, Belle Aire (often confused with a plantation about five miles inland with the same pronunciation but the name
Bel Air which was owned and operated by the Ewell family) was between the
Occoquan River and Neabsco Creek near the ferry (later bridge) conducting the
King's Highway across the Occoquan River and which became
Woodbridge, Virginia. It had been the property of William Linton a previous husband of this man's mother, Susan, who married Benjamin Grayson by 1732. William Grayson received his first schooling locally under Charles Tyler, and later became known for familiarity with Latin and Greek as well as English history. His guardian allowed his education in Philadelphia at the
University of Pennsylvania, and (after graduating) William Grayson sailed to England. Although some family sources claim he studied law for two and a half years, and received his degree from the University of Oxford, neither university nor Inns of Court documentation exists to support that tradition, so he was likely apprenticed to British merchant bankers like
William Lee. When his brother and guardian Benjamin faced financial troubles in 1762 (so that he mortgaged his entire estate to his brother Spence), William returned home and as his need for a guardian ended, found that his spending abroad had also diminished the capital he had inherited. Grayson married Eleanor Smallwood, a sister of
Maryland Governor William Smallwood, who survived him. They had four sons (Frederick, George, Robert and Alfred) and a daughter (Hebe). ==Return to the Virginia colony==