The population of West Chester on December 21st 2011 is approximately 18,521. (Extrapolated from a 2000 US census population of 17,861 and a population of 18,461 in 2010.)
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545.02 kilometres (338.66 miles)
It is 113.65 miles according to MapQuest.
Google Maps estimates the driving time as 8 hours and 29 minutes.