We used to go to a place called Loch Lyme Lodge in Lyme, NH.. It allowed dogs (I'm pretty sure it still does but you'd want to check just to be sure, as it has switched management). It's on about 100 acres of wood and meadow and it's on Post Pond. They have docks, row boats, kyaks, a float in the water, a small beach, and beach chairs on the water. Across the street is the lodge, and it consists of a bunch of small cabins that you can rent for a week or more and also a white house that you can rent rooms in for a day or more. If you sleep in the white house, they have a little restaurant kind of thing below it that feeds you and of course you can still go there and eat at it if you're staying in a cabin! They also have a little ice cream shop, which is my personal favorite.

Along with all that, they have a recreation cabin with a TV and a bunch of good older movies and a ping pong table, swing set, etc. There's also a tennis court and miles of trails through the woods and a meadow with a soccer field, basketball court and baseball field too. And the dogs are allowed to go swimming, but I think it's better if they go swimming in the morning or evening when there aren't as many kids in the water.. or at least swim in a less populated area. Oh! and across the pond is a huge rock we used to call "Alligator Rock" because it's shaped like one and you can canoe out there and have a picnic. The lodge is in walking distance from town where there are flee markets and a cute general store, and along the way there are the prettiest wildflowers and views. There are also great hiking places around the lodge. Sorry to keep babbling on but seriously, this place is fantastic!
here's the website if you're interested:
http://www.lochlymelodge.com/