I'd recommend something in Otsego County surrounding Cooperstown. The nearby lake would be Otsego Lake then you can go to Cooperstown for the village stuff as well as the baseball museum and Fenimore arts museum. If you want Hudson River area, check out Tivoli or Germantown (or Chatham further inland with farms).
FYI the Columbia County Fair is coming up Sept. 2-7 which would make Chatham or Kinderhook good options for that timeframe (or Germantown which is 45 mins away from the fair):
http://www.columbiafair.com/index.php