John Posey was a captain of the 2d company of artificers in the 2d Virginia Regiment in the latter 1750s. Posey, whose home, Rover’s Delight, stood near the Potomac River about a mile southwest of Mount Vernon, was a regular in GW’s social circle in the 1760s, often joining him in fox hunts. Posey farmed a plantation of about 400 acres and operated a public ferry from a landing near his house across the Potomac to Maryland, where he had many personal contacts. In 1769 John West, Jr., sued Posey, claiming title to the six-acre strip of land between Dogue Creek and Little Hunting Creek that included the ferry. GW acquired title to the land in 1772.

Posey was married first to Martha Price Harrison, and the couple had at least four children. Their daughter, Amelia ("Milly"), a friend of Martha Parke Custis, apparently lived at Mount Vernon for several years in the 1770s. She remained there until nearly the end of the Revolutionary War. Posey's son, John Price Posey, was a childhood friend of John Parke Custis, and was later placed in charge of the latter's plantations. Their other two children were Hanson and St. Lawrence. John Posey was later briefly married to Elizabeth Adair of Maryland.

GW's ledgers show several transactions with Posey. In his account with Posey, GW entered charges in “1757 & 58” against Posey “To Sundry Work done by my Carpenter valud to” £30, as well as additional charges of £6.18 and £18.15 for wheat (Ledger A, 14). GW’s carpenter built for Posey among other things a kitchen. GW also entered cash payments by Posey to GW's overseer Humphrey Knight of £12.10, £5, and £25 (Ledger A, 14). GW also lent money to Posey on several occasions. For instance, in 1756, GW lent £2 to Posey at Winchester (see Ledger A, 14), and in 1761, Posey borrowed £5 in Williamsburg (see Ledger A, 92).