Thousands, obviously. The Earth is only about 6000 years old.
Historical accounts by witnesses of live dinosaurs. There's a whole chapter of them in the book "After the flood", by Bill Cooper (chapter 10, Dinosaurs from Anglo-Saxon and other Records). "The early Britons, from whom the modern Welsh are descended, provide us with our earliest surviving European accounts of reptilian monsters, one of whom killed and devoured king Morvidus (Morydd) in ca 336 BC."
I can't vouch for the following site (its probably non-Christian), but it seems to have a bit of detail on this king. There are many, many other accounts of encounters with creatures described in a way we would describe dinosaurs today.
Dinosaurs of Ancient Britain Part 1