The Southern Tier is a geographical term that refers to the counties of upstate New York State west of the Catskill Mountains along the northern border of Pennsylvania, with the exception of the counties in the far west of the state near the city of Buffalo.

The region is bordered to the south by the Northern Tier of Pennsylvania, and together these regions are known as the Twin Tiers.

The counties (and major cities and towns) generally included in the Southern Tier are:

Delaware County	– Village of Delhi
Otsego County	– Oneonta
Chenango County	– Norwich
Broome County	– Binghamton, Endicott & Johnson City
Tioga County	– Owego, Waverly
Chemung County	– Elmira
Steuben County	– Corning, Bath & Hornell
Allegany County	– Wellsville

(The two western counties, Cattaraugus County and Chautauqua County, which also form the border with Pennsylvania, are sometimes referred to as Southern Tier counties.)

The Southern Tier is generally hilly without being mountainous. Both the Delaware and Susquehanna rivers flow through the Southern Tier in their upper reaches.

The largest city in the region is Binghamton, near which is located Binghamton University (formerly the State University of New York-Binghamton), one of the largest components of the SUNY system. Like most of the rest of upstate New York, the Southern Tier has experienced a net population loss over the last several decades. This is mostly likely due to decline in the manufacturing industries that once flourished there, its relative inaccessibility from major cosmopolitan centers, and a generally unfavorable climate compared to more flourishing regions of the country.