We have rented a cabin for july 4, do we check in at park office? What happens if we get there after office closes please?

You will go through the first gate. They will charge you 9 dollars for out of state and 7 dollars for in state. Then go to next check in and they will check you in. Make sure you call them ahead of time your arrival and let them know you will be late. And they will make arrangements for you to get the key. They are great people. My wife and I go there all the time. But be sure to call if you arrive after hours

Check in at the front gate if the main office is closed.

Excellent response!

Thank you all for the answers!