From The Art and Popular Culture Encyclopedia
The Hudson Valley refers to the valley of the Hudson River and its adjacent communities in New York state, United States, from northern Westchester County northward to the cities of Albany and Troy. Historically a cradle of European settlement in the northeastern United States and a strategic battleground in colonial wars, it now consists of suburbs of the metropolitan area of New York City at its southern end, shading into rural territory, including "exurbs," farther north.
Geographically, the Hudson Valley could refer to all areas along the Hudson River, including Bergen County, New Jersey. However, this definition is not commonly used and the Tappan Zee Bridge is often considered the southern limit of the area. Though Westchester County is often classified as part of the region, Westchester residents who live at the southern end of the county (and especially the parts closer to the Long Island Sound than the Hudson River) generally do not associate themselves with the region, unless their town includes Hudson River banks. Including all of Westchester County in the definition of the region would seem unusual to many and seems like something one might only read in a travel guide. In fact, there is a road sign on the New York State Thruway in Yonkers that suggests that the "Hudson Valley region" is located somewhere farther to the north and west along the Thruway.
Another geographical issue involves the northern extent of the Hudson Valley, and specifically, the northern half of the Hudson River, which does not flow through the valley commonly called the Hudson Valley. Although the southern half of the river flows through the center of a great glacial valley which extends from Lake Champlain to New York City, the northern half of the river runs through the Adirondack Mountains. The great glacial valley continues, apart from the Hudson, farther north, where it is known as the Champlain Valley. Thus, the great glacial valley is known as the Champlain Valley in its northern extent, and the Hudson Valley in its southern, changing names at a point slightly north of Albany. The exact spot can possibly be pinpointed at Fort Edward, which is where the Champlain Canal leaves the Hudson River and goes on its own to Lake Champlain. In common usage, however, the city of Troy appears to be the northernmost point of the Hudson Valley, as that city contains the first lock on the Hudson, keeping deep-water ships from navigating farther north. In fact, the Hudson Valley and Champlain Valley are only two parts of the much greater Great Appalachian Valley.