Allegheny

County, southwestern Pennsylvania, U.S., consisting of a hilly region on the Allegheny Plateau bounded to the southeast by the Monongahela and Youghiogheny rivers and to the northeast by the Allegheny River. The Ohio, Allegheny, and Monongahela rivers converge in the centre of the county to form an area known as the Golden Triangle; this was a strategic point of contention