The campground is about 45 minutes from town. You will likely loose cell service 15-20 minutes into your drive so get your directions now.
The campground is on the left-hand side of the road (the river side), some maps may incorrectly show it on the right.

Once you pull in, the wedding will be towards the left. 

Google Maps
https://www.google.com/maps/place/Hemple+Creek+Campground/@48.078437,-121.745681,17z

Apple Maps
http://maps.apple.com/?q=48.078194,-121.744431&sll=48.078194,-121.744431
 
lat/long location
48.078430, -121.745981