Prior to COBRA, there used to be a lot of state-based rules regarding the continuation of insurance. COBRA made most of them obsolete.
No state at present has a 30-days-after-termination law. At one time post-COBRA, Texas had a law that required coverage to continue to the last day of the month in which employment ended, but when I went looking for it recently I not only couldn't find it, but none of my Texas colleagues could find it either. So as Patty says, it may have since been repealed.
No other state to my knowledge has an actual law dictating how long coverage continues after termination. It depends entirely on what the plan document says. In my experience, and I have a LOT of experience, about 50% of plans cover till the last day of the month in which employment ends, and the other 50% terminate coverage on the last day of employment, but it's policy specific, not state or Federal law.