Fairly last minute trip, but within a couple weeks of our trip, I was able to find one last available site. Woohoo! 

Nice open grassy site - drove right up and had a great breakfast, couple nights great rest while we explored the area. 

Notes:

primitive site, outhouses only, so bring your sun shower.

And it is in the northeast of the park, a lonnnng leisurely dirt road trek down to trailhead for Chimney Pond trail and summiting Katahdin. Made sure we left by 3am to get to the main gate by 6am. IF you stayed overnight in the park, you can roll right into the parking lot before the main gate opens (there WILL be a line of cars waiting to get in as soon as the gates open, and once the lot is full it's full – no more preference to those who stayed overnight anywhere in the park)

Baxter is one of the most pristine, magical and majestic public lands in the US, always worth a visit. My fave time of year is Sept. here.