Ferdinand Vandiveer Hayden
It is generally accepted that the first discovery of dinosaur remains made in North America was in 1854, by Ferdinand Vandiveer Hayden during his exploration of the upper Missouri River. Near the confluence with the Judith River, Hayden's party recovered a small collection of teeth which were later described (in 1856) by Joseph Leidy. Three of the specimens described were dinosaurs - Trachodon, Troodon and Deinodon (notice the use of 'don' meaning 'tooth'.)
This was the first published description of dinosaur remains in the US. Leidy recognised that Trachodon was a creature similar to Iguanodon