Jefferson County has several unique historic places. One of the most unique is the Mastodon State Historic Site. Did you know that huge Mastodons roamed Missouri? Yes they did and apparently in large numbers! Go check it out! Jefferson County is also home to two of Missouri's first governors. Thomas C. Fletcher was Missouri's eighteenth and the first native born governor. His home, the Thomas C. Fletcher House is located in Hillsboro. Daniel Dunklin was Missouri's fifth governor and his gravesite, the Governor Dunklin Grave State Historic Site can be found in Herculaneum. Below is a list of some of the other historic sites found in Jefferson County.