Letchworth is a great State park, it's nickname is the "Grand Canyon of the East", it is well kept with specified pet loops so those who have no pet are not forced to deal with a barking dog next door. The trail system throughout the gorge is Letchworths main claim to fame, it's great for hiking or biking. There's also an olympic sized swimming pool but it costs extra and is too far to walk to from the camp grounds.
Russ-Bett,
We are halfway between Rochester and Canandaigua, just off I90 exit 45. Here are what I consider the best RV parks in the immediate area.
Canandaigua KOA-
http://www.koa.com/where/ny/32140.htm
A standard KOA about 3 miles north of the city of Canandaigua, in a nice countryside setting. Last year we stayed it was about $32 per night w/ electric. Only negative I can think of is that it is so open that wind gusts can be high.
Bristol Woodlands-
http://www.gocampingamerica.com/bristol/index.html
A small campground open 2-3 years ago in a rural area approx. 5 miles Northwest of the city. Stayed there the first year they were open. Rates were in the $15-20 per night range w/ electric. I was impressed with the potential at the time and have talked to others who have visited more recently and have commented on how nicely kept and quiet the campgrounds are.
Those are the closest to Canandaigua. Hope this helps. Let me know if I can answer any other questions.