You haven't been to downtown Houston after 8:00pm. Yes, zombies DO exist.
They aren't created by meteorites or viruses like in the movies. They are created by people destroying their minds on drugs, having ZERO education, learning to take no responsibility for themselves or others, being morally depraved... so all they do is shamble around aimlessly without any soul or purpose. Those are the zombies.

... and yes, there are thousands of them and they do wander the streets of Houston after dark. If SHTF, watch their numbers grow to the tens of thousands. They are just smart enough to figure ways to break into those yuppie loft apartment buildings too.

Dayton, Texas is a great town for watching zombies. Just pull up a lawn chair near Highway 90 at night... and watch the zombies wander across the highway in search of alcohol (or whatever they are after)... and then stumbling back across the highway to their apartments or trailers.