This campground is clean and well kept. Lots of families here. Swimming in a pond or a short drive to a bigger lake (camping pass covers both). One of my favorites. It's kind of a hidden gem in north central Massachusetts.
Otter River State Park is located in Winchendon, in north central MA proximate to the NH border. The park was certainly lovely, facilities clean and my stay pleasant. Sites were a bit small. The hiking trails in and around the camp trail were nice, but not overly remarkable. Don’t recall there being a ton to do in and around the neighboring towns. Really, this is a good, low-key spot for families looking to spend a couple days out of the city. It’s about a 1 1/2 hour drive from Boston. Kids can play safely and bike throughout the grounds.
I went with a group of 4 in mid-July. The campground was clean and well-maintained but the sites are quite small and close together. There were a ton of kids and it was pretty noisy until about 11pm and then starting again around 7am.
The hiking in the area isn't great. There are a few trails but not a lot of interesting features and very little elevation change. The biggest pro is that it's only an hour from Boston.
Checking in is a big process here - it took about 5-10 minutes to get past the front gate because they ask for so much info about your party.
One additional perk is the rangers leave you completely alone.
With the exception of a handful of the sites at this campground (mainly, the ones on the pond that go exceptionally quickly), the sites are too small, too close together, and there are a ton of kids. From my site, I could hear our neighbors blasting their radio all day (even after quiet hours), and another group of people somewhere further away singing pretty much all night.
The pluses are it's relatively close to Boston and Worcester if you need a day or two away (and can book one of the quieter sites), the bathrooms and showers are clean (and free), and the rangers are exceptionally friendly.