I'm located in The Woodlands which is about 40 miles from Houston. I know some areas but the ones I go to might be a bit of a drive for you.
If you can make it you might try going to Lake Houston Park which is located in New Caney. It's a 40 minute drive from where I live but it's a nice place to go especially if you're into camping. It's one of the largest parks in the area and there are parts of it where people never actually go. The plus sides of this is that there are herps and animals there that can't survive in smaller parks. The bad side is that many animals are not used to people as much (they don't get fed by people) so you may at first think your spottings are a little sparse.
I intern there and was there a lot over the summer. I'm often there working at the nature center on weekends. They've got a huge collection of native animals and so there's tons of live snakes, turtles, fish etc on display. It's a huge nature center that's very well furnished and stuff. Only a couple years old too. There are presentations on most saturdays so if you ask you can find out when there'll be one on snakes/reptiles.
As far as species you'll find there... I see a lot of ribbons, ratsnakes, racers, and copperheads. You can also find cottonmouths, water snakes, crayfish snakes, milk snakes, hognose snakes, green snakes, and others but those are irregular sightings. If you go spotting at night you'll probably find some cool stuff.
If you're going there then any day is fine except monday, tuesday, and wednesday (the naturalist who does the nature center isn't there on monday and tuesday and it's often closed part of wednesday). Just ask to talk to Crystal and she can give you any pointers you might want. If you refer to Emily(me) she'll know who you're talking about. Fee is $3 per person.
I'm at a lot of local areas but if you can drive to Humble there's Jesse Jones Park (Mike Howlett's the reptile guy there) and if you drive to Huntsville there's Huntsville state park. Haven't really been around there but that's located in Sam Houston National Forest so it's got to have some good herps. Sheldon Lake State Park is located in Houston but I haven't been there. I'm pretty sure they've got alligators there though.
Please remember if you're at parks the wildlife is protected so taking anything is prohibited. But they're still good for herping sightseeing.
If you have any other questions you can message me. I'm pretty good about checking my email.
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1.0 sumatran short tailed python
0.1 ball python
0.1 rosy boa
0.1 corn snake
1.0 mexican king snake
1.1 buttermilk racers
0.0.2 texas rat snakes
0.0.1 broadbanded watersnakes
0.0.2 yellow bellied watersnake
0.0.1 diamond back watersnake
0.0.1 blotched watersnake
0.0.1 ribbon snake
0.1 Texas brown snake
0.0.1 western cottonmouth
0.0.1 southern copperhead
0.0.1 rattlesnake
1.0 bearded dragon
1.0 leopard gecko