Castle Hills, The town borders Uptown San Antonio to the west and is about 7 miles (10 miles driving distance) north of Downtown San Antonio. According to the United States Census Bureau, the city has a total area of 2.5 square miles (6.5 km2), of which, 2.5 square miles (6.5 km2) of it is land and none of the area is covered with water. Castle Hills is an independent municipality, completely surrounded by the city of San Antonio. It is bisected into a northern and southern half by interstate highway loop I-410. It is located at the southern end of Northwest Military Highway, the northern end being located at U.S. Army Camp Bullis.