The digital Supplement contains figures in original size (TIFF) & digital data (SHP, CSV). The data can be also found in the linked GitHub repository https://github.com/sdam-au/perachora-medit-arch/. Abstract The Perachora Peninsula Archaeological Project held its first season of intensive surface survey from 12 January to 2 February 2020, during which time we focused on the region called the Upper Plain, situated above the sanctuary of Hera, which was in use from the 8th to the 2nd century BC. The nature of this area has been disputed, with Humfry Payne seeing it as a substantial town, while Richard Tomlinson referred to it as “a sporadic scatter of structures.” In order to clarify the nature of the settlement we employed a two-pronged effort: first to verify and document the legacy data in Tomlinson’s plan of the area, and second to conduct intensive surface survey from the boundary of the sanctuary to Lake Vouliagmeni. Within three weeks, our teams measured, photographed, and took the coordinates of nearly all the structures on Tomlinson’s plan, which included domestic structures, a small temple, and an extensive waterworks system, and several that had not been previously recorded. Building A 1 and the Fountain House were cleared and recorded using photogrammetry. The survey’s finds informed our legacy data verification efforts. Densities across all land types were high: nearly 23,000 artefacts were counted, and all but nine survey units produced artefacts. A preliminary analysis of the ceramics indicates a consistent habitation from the Archaic through the Classical period. Concentrations of miniature votives and fine wares were also found on hillsides, possibly indicating open-air shrines. Our work also highlights the need to conserve the structures in the Upper Plain.