Most of the area was traditionally part of Buckinghamshire and formed over many years by the amalgamation of villages along the Great West Road from London in the east to Bath and Bristol in the west. The first recorded uses of the name occur as "Slo" in 1196, "Sloo" in 1336, and "Le Slowe", "Slowe" or "Slow" in 1437. The name may have derived from the various sloughs in the area caused by rain water flowing from the Chilton Hills to the River Thames, or it may refer instead to Sloe bushes growing in the vicinity. The name first seems to have applied to a hamlet between Upton to the east and Chalvey to the west, roughly around the 'Crown Crossroads' where the road to Windsor (now the A332) met the Great West Road. Along with Salt Hill, these settlements formed the parish of "Upton-cum-Chalvey".