East Granby is in the Farmington valley, with the Farmington River passing along the southern border of the town. The Metacomet Ridge, a mountainous trap rock ridgeline that stretches from Long Island Sound to nearly the Vermont border, runs through the center of the town, cutting off Salisbury Plain to the east, which used to lie under the ancient, glacial Lake Hitchcock. High points on the Metacomet Ridge in East Granby include Hatchet Hill and Peak Mountain; the latter offers a bird's eye view of the historic Old Newgate Prison. The Metacomet Trail traverses the ridge.