Okay...great. Thanks for the additional information. I really appreciate it.
If you just started taking him to that park last week, and it's a new place, then the odds of it being kennel cough are pretty high.
The good news is that kennel cough generally only gets so bad before it gets better on it's own, so I don't feel like you need to rush him to the emergency vet or anything tonight, but I absolutely think that taking into consideration his history, it might not be a bad idea to give your vet a call tomorrow, just to be on the safe side and see if they want to get him on some antibiotics, just to be on the safe side.
You can also talk to them about giving him the vaccine...it'll protect him against kennel cough that he encounters after this if you're going to be taking him to that park with some regularity.
And of course, it goes without saying that if he gets sicker tonight, or if he starts to show any signs of an obstruction such as vomiting immediately after eating/drinking anything, becomes lethargic or anorexic, then you should have him seen before your vet opens tomorrow.
I hope this helps.