The Hillsborough River is a river located in the state of Florida in the United States. It arises in the Green Swamp near the juncture of Hillsborough, Pasco and Polk counties, and flows 60 miles (97 km) through Pasco and Hillsborough Counties to an outlet in the city of Tampa on Hillsborough Bay. It includes 4 nature trails extending for over 7 miles (11 km), making it popular among hikers. The name Hillsborough River first appeared on a British map in 1769. At the time, the Earl of Hillsborough was the British Secretary of State for the Colonies, and thus controlled the pensions of the surveyors working in the American colonies, which included East Florida.

Hillsborough County is located in the west-central portion of the U.S. state of Florida. In the 2020 census, the population was 1,459,762, making it the fourth-most populous county in Florida and the most populous county outside the Miami metropolitan area. A 2021 estimate has the population of Hillsborough County at 1,512,070 people with a yearly growth rate of 1.34%, which itself is greater than the populations of 12 states according to their 2019 population estimates. Its county seat and largest city is Tampa. Hillsborough County is part of the Tampa–St. Petersburg–Clearwater Metropolitan Statistical Area.