The "Treasurer's Plantation" was a plot of land patented by George Sandys. Sandys arrived in Virginia in 1621, and was served as the colony's treasurer (the date isn't clear, as he is stated as the Treasurer in a report dated July 24, 1621). Sandys had stock in the Virginia company worth 100 acres, and transported 4 other people, giving him an additional 200 acres, giving him a sizable grant near Jamestown.

Sandy's plot is mentioned here in Hatch's The First Seventeen Years: Virginia 1607-1624. You can also read a description of the patent here.

"three hundred acres of Land scituate & being on the other side of the river opposite against James Citty and abutting Westward on the land of John Baineham and Eastward on the land of Edward Grindon of both which devidents hee is now actually possessed &c."