Boston, MA area camping....

I'd also recommend Wompatuck state park in Hingham. I was there for 8 nights in early July. It's a very nice shaded campground, with plenty of space between sites. There is no water at the sites (or sewer connections), but there are water spigots throughout the park. I was running low on water and was able to run a hose from my MH to a nearby spigot, to add water to my tank. They only have 20 AMP service on their sites with electricity, but I was able to get by without any problems.
As mentioned earlier, the commuter boat out of Hingham to Boston (and Logan airport) is a nice relaxing, stress free way, to get into Boston