You have tons of old places in Ulster. Start at the Kingston Historical Society, bound to be lots of good info there. Lots of small picnic areas along the river too.
Good luck.
Welcome to TreasureNet from a native Upstater... Ulster County was formed on 1 November 1683. Something is really very wrong if you cannot find someplace awesome to detect there!
I guess it depends on just what you want to detect...
For example... your own yard, local school grounds, or park might be perfect.
Or, if you are into relics, your area is loaded with history. I'm going to assume you have some idea of your own local county history... but for those not knowledgable: "The county was settled by the Dutch as early as 1616. Tradition says that at a very early period there were settlers upon the Minisink on the Delaware, who transported some valuable minerals by the road along the Rondout to the North river. This county appears to have suffered more from Indian hostilities than any other portion of the country while under the Dutch. The quarrel appears to have arisen on account of an Indian woman being killed when stealing peaches from a garden. The county is divided into 14 towns." Source: http://www.usgennet.org/usa/ny/county/ulster/