Poplar Cottage lay within the parish of Washington, which in the late 17th century had a population of about 400 to 450. Land in Washington was divided between two manors, Washington and Chancton, and both manors had rights of common on Washington Common, as well as having common land elsewhere within the parish. The manorial status of Poplar Cottage has always been problematic to those attempting to research the history of the house. A map of the manor of Washington dated c.1739 shows the cottage set on its own on the edge of Washington Common and outside the boundary of the manor on land held by Sir Robert Fagg, lord of the neighbouring manor of Wiston. Additional research has now established that in 1715 Fagg bought a chunk of the former demesne lands of Chancton manor from the lord of Chancton, James Butler. This chunk included 85 acres in the north of Findon and 70 acres in Washington. Although the exact bounds are unclear, the 70 acres appears to have comprised the land to the south of Washington Common (and so including Poplar Cottage), extending to the top of Chanctonbury Hill. By the 19th century this land, and Poplar Cottage, had been incorporated into the Wiston estate, owned by successive members of the Goring family.

The court book for the manor of Chancton beginning in 1603 records several presentments in the manorial court in the early 17th century for the illegal erection of cottages on manorial waste. For example, in 1603 the court presented that ‘William Wilkin has encroached on a parcel of the lord’s waste called Washington Common and thereupon has built a certain cottage without licence’. And in 1605 five tenants were presented together for building cottages without licence on manorial waste and each fined 6s 8d, and ordered to pull their cottages down or face a further fine of 10s. The earliest surviving court book for the manor of Washington begins in 1682 by which time there were at least half a dozen wasteland cottages, all copyhold properties. Such cottages can be identified either because they are described as ‘formerly part of the waste’ and/or because of their location on or besides manorial waste.