I always thought it was in Ohio but is that wrong?

It could be...it could be anywhere. In seven seasons, no state is mentioned.

I think they deliberately kept the state's locale uncertain but with the vague idea that it was somewhere in the Midwest so the viewers wouldn't have too much trouble relating to it (same way 'LITB's Mayfield never got a state name and Lassie's original families were in an unnamed rural locale in an unnamed state where the only major city was called 'Capital City' (NOT 'the capital city').

Oddly enough, they moved to North Hollywood, California after seven years but, amazingly enough, stayed every bit as vanilla and anti-counterculture as possible despite being literally in the midst of it!

http://bryantpark.org/

Bryant Park is a fictional town like Bedrock (The Flintstones), Springfield (The Simpsons), Mayberry (The Andy Griffith Show), Peekskill (Facts of Life), Gotham City (Batman), Hooterville (Petticoat Junction and Green Acres), Glenlawn (Gimme A Break!), and Mayfield (Leave It To Beaver).

Peekskill is most definitely real. My girlfriend went to a community college one town over.

Peekskill is most definitely real. My girlfriend went to a community college one town over.
Sorry, my bad. But you get the idea, right?