Should I use "in" or "at"

ccpShould I said

You should say: The factory is located in the State of California.

CB

From the sense of your sentence, I would choose "The factory is located in the State of California."
Depending on the rest of the text not shown, "The factory is located in California State." might also be acceptable.
I doubt that there would be a factory within the University called "California State".

ccpShould I said say

If by "California State" you really do mean "California State University", say

The factory is located at California State.

But is there really a factory there?

Besides, there are many branches of that university, so unless you're speaking with people who know exactly

Thank you all!

To CalifJim's point: I used the State of California as an example of what I tried to write. I could have used any other state in my example, therefore no, I didn't mean the University. So "... in the state of ... " would be the right form, as you guys kindly advised.

Thank you!

If you're writing in the U.S. (where you can assume that people know that California is a state), the simplest would be to say "The factory is located in California."

EDITED TO ADD: or simpler yet -- "The factory is in California."