Hillsborough County was created on January 25, 1834, from Alachua and Monroe Counties, during the U.S. territorial period (1822–1845). The new county was named for Wills Hill, the Earl of Hillsborough, who served as British Secretary of State for the Colonies from 1768 to 1772. The County was created through efforts by Augustus Steele.

The county’s 1834 area was much larger and included eight other present-day counties: Charlotte County, DeSoto, Hardee, Manatee, Pasco, Pinellas, Polk, and Sarasota.

The last significant change in Hillsborough County’s borders was the separation of its western section to create Pinellas County in 1911.

On New Year’s Day in 1914, the St. Petersburg-Tampa Airboat Line initiated the first scheduled commercial airline service in the world, from St. Petersburg to Tampa.