This is one of the biggest caterpillars we have ever seen! User 'boomerangsbyVic' found it on his property and asks the same question we do: Does anybody know what kind of caterpillar this is?!
That is a hickory horned devil, moth caterpillar one of the largest in the Americas
I disagree with AndrewJames1957 ... I feel it is more like the Hyalophora cecropia - https://en.wikipedia.org/wiki/Hyalophora_cecropia