| Unadilla River | |
| Name Other: | Tianadara |
| Pushpin Map: | New York |
| Pushpin Map Caption: | Location of the mouth of Unadilla River |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | New York |
| Subdivision Type3: | Region |
| Subdivision Name3: | Central New York |
| Length: | 71miles |
| Source1 Location: | NE of Millers Mills |
| Source1 Coordinates: | 42.9325°N -75.0275°W |
| Mouth: | Susquehanna River |
| Mouth Location: | Sidney |
| Mouth Coordinates: | 42.3168°N -75.41°W |
| Mouth Elevation: | 961feet |
| Progression: | Unadilla River → Susquehanna River → Chesapeake Bay → Atlantic Ocean |
| Tributaries Left: | Campbell Brook, Wharton Creek, Butternut Creek, Rogers Hollow Brook |
| Tributaries Right: | North Winfield Creek, West Branch Unadilla River, Button Creek, Beaver Creek, Tallette Creek, Center Brook, Mill Brook, Great Brook, White Store Brook, Kent Brook, Guilford Creek, Peckham Brook |
The Unadilla River is a 71adj=midNaNadj=mid[1] river in the Central New York Region of New York State.[2] The river begins northeast of the hamlet of Millers Mills and flows generally south to the village of Sidney, where it converges with the Susquehanna River, which drains into the Chesapeake Bay,[3] a bay of the Atlantic Ocean.
Most of the length of the Unadilla forms the western border of Otsego County and the eastern borders of Chenango and Madison counties, all in New York. This border made up a significant portion of the Fort Stanwix Treaty Line of 1768. It was meant to establish the border for an Indian reserve, beyond which European-American settlers were not supposed to go. Settlers resented British efforts to control their movements, and continued to encroach on Native American territories.
The Unadilla has two branches which join at Unadilla Forks on the Otsego-Madison County border.
The Unadilla's tributaries, from north to south, include:
from the west, at New Berlin
from the east, at New Berlin
Unadilla has had various spellings and alternate names, particularly in the 18th century:[6]
Vaughan's 18th century Chorographical Map