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Separately, the two halves of the Twin Tiers region are known as the Southern Tier region in the state of New York and the Northern Tier region in the Commonwealth of Pennsylvania. Somewhat counterintuitively, the Southern Tier is in fact further north than the Northern Tier, and conversely the Northern Tier is south of the Southern Tier. This is because the "Northern" and "Southern" designations are relative to the states in which they are located, not relative to each other.
The region is predominantly rural and contains many small towns. It is usually defined as including the following counties:
|Northern Tier||Southern Tier|
In an oddity, McKean, Potter and (less often) Cameron Counties refer to themselves as part of the Twin Tiers but almost never consider themselves part of the Northern Tier, instead going by the name "Northern Pennsylvania." There is often significant "bleedover" in regions: for instance, the western part of the region (McKean and Potter Counties) often will associate themselves with St. Marys, a city larger than any city in that area but in Elk County, just south of what is considered "Northern Tier" by any standard.
The region was historically a disputed territory in the history of the United States prior to its founding. The Northern Tier was claimed by Pennsylvania Colony and Connecticut Colony, while the Southern Tier was claimed by Pennsylvania, Massachusetts Bay Colony and New York Colony. Various treaties and land sales eventually placed the Northern Tier in Pennsylvania's hands and the Southern Tier in New York's.
Though the region has much in common, there are a few differences. Most notable is the choice of sports teams: the Southern Tier has a tendency to support Buffalo and, in the eastern part of the state, New York City teams, while Northern Tier areas are more likely to root for teams from Philadelphia or Pittsburgh.