Physical Characteristics. Hillsborough County is on the Gulf coast and is bordered by Tampa Bay and by Pinellas, Polk, Manatee, and Pasco counties. The county has 1052.86 square miles of land and 39.25 square miles of water for a total of 1092.11 square miles. The average January temperature is 60.4 degrees Fahrenheit, and the average August temperature is 81.5 degrees Fahrenheit. The average annual rainfall is 48.48 inches.
History. Hillsborough County was established 1834 from St. Johns County and named for Wills Hills, the Earl of Hillsborough.
