Doubtful News examines surveys
It's weird, in a way, to ask if people "believe" in a creature. The creature is either real or not, and it doesn't care how many people think it's out there. Neither, properly, does science: reality is independent of polls. But polls are taken, and are interesting to peruse. Here Doubtful News looks at recent polls on Bigfoot and Nessie. So, to quote a blog that quotes the surveys (Okay, I admit this is the lazy way to do it, but the facts are the same): "three-in-ten Americans (29%) and one-in-five Canadians (21%) think Bigfoot is “definitely” or “probably” real." and "17 per cent of Britons believe the Loch Ness Monster is “definitely” or “probably” real — 24 per cent in Scotland." Sharon Hill wonders to what extent the numbers are skewed by recent films, TV, etc. which of course they could be. (Someone should take a poll on mermaids before and after the upcoming Animal Planet science fiction show about a mermaid being found. ) She also asks if "real" necessarily refers to the physical creature, although I think most of those polled assume that's what they were being asked.
Grover Krantz once explained, "I don't believe or disbelieve. I have certain knowledge that causes me to conclude." Whether one agrees with the late Dr. Krantz on his conclusion, the fact that a large number of people believe these creatures exist is very interesting by itself. If you believe the surveys are real.