1/3 of a mile up the Mt. Aire trail there are a few premade dispersed camping spots. 1 is good for groups of 3 tents with a nice big fire pit and the others are smaller for 1 or 2 people sharing a tent. They are right off the trail but the trail is somewhat busy, you won't be completely alone until after 10pm or before 5 (trail runners are crazy). 

It's hard to walk in as if you are 'car camping' worth it to backpack everything in one go, there is a creek and it's cool in the canyon, plus you really can't beat a camp spot that is only 20 minutes outside of town and that no one ever goes to. People don't seem to camp in Millcreek that often, I'm not sure why. 

I would recommend setting up at Mt. Aire, and then camping to the summit (45 minute uphill trek) for sunset or sunrise, both are beautiful.