Jefferson County has many interesting historic places, but one of the most unique is the Mastodon State Historic Site. Did you know that Mastodons roamed Missouri? Yes they did and apparently in large numbers! Go check it out! Two of Missouri's first Governors are from Jefferson County, Daniel Dunklin, the fifth governor, and Thomas C. Fletcher, the eighteenth and Missouri's first native born governor. The Thomas C. Fletcher House can be found in Hillsboro and the Governor Dunklin Grave Historic Site can be found in Herculaneum. Below is a list of some of the other historic places in Jefferson County.