Drive
12 Mike beach is a drive in campground that you can reserve through recreation. Gov. Make sure you reserve before you go. There may be a Backcountry campground named that as well but I would guess the main one you are talking about is the drive in one with 30 + sites. Just stayed at site 28 last week. Very nice.
There are 36 drive-in sites at Twelvemile Beach. There are also Backcountry (hike in) sites .3 miles away at Benchmark.
12 Mile is a drive in but the North Country trail runs through it if you want to hike in.
Both
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