Wilkes-Barre (/wɪlksˈbɛər/ or /-ˈbæri/) is a city in the Commonwealth of Pennsylvania and the county seat of Luzerne County. It is one of the principal cities in the Scranton–Wilkes-Barre–Hazleton, PA Metropolitan Statistical Area. Located at the center of the Wyoming Valley it is second only to the nearby city of Scranton. The Scranton–Wilkes-Barre–Hazleton, PA Metropolitan Statistical Area had a population of 563,631 as of the 2010 Census making it the fourth largest metro/statistical area in the state of Pennsylvania. Wilkes-Barre and the surrounding Wyoming Valley are framed by the Pocono Mountains to the east, the Endless Mountains to the west and the Lehigh Valley to the south. The Susquehanna River flows through the center of the valley and defines the northwestern border of the city. Wilkes-Barre was founded in 1769 and formally incorporated in 1806. The city grew rapidly after the discovery of nearby coal reserves and the arrival of hundreds of thousands of immigrants. The city reached the height of its prosperity in the first half of the 20th century when its population reached just over 86,000. Following World War II, the city's economy declined and the Knox Mine disaster accelerated this trend when large portions of the area's coal mines were flooded. Today the city has a population of 41,498, making it the 13th largest city in the Commonwealth of Pennsylvania.