Ridgely was born in Prince George's County, in the Calvert / Lord Baltimore's proprietary colony of the Province of Maryland, and still a minor at the death of his father in 1705. He inherited the estates "White Wine" and "Claret" from his grandfather Hon. John Dorsey, Capt. ( – 1715), although he never lived at either. At the time they totaled 1,400 acres (5.7 km2) between them, and Ridgely later resurveyed them into 2,145 acres (8.68 km2) by adding some surplus land.