York County is a county in the Commonwealth of Pennsylvania, United States. As of the 2020 census, the population was 456,438. Its county seat is York. The county was created on August 19, 1749, from part of Lancaster County and named either after the Duke of York, an early patron of the Penn family, or for the city and county of York in England. The county is part of the South Central region of the state.

York County comprises the York-Hanover, Pennsylvania Metropolitan Statistical Area, which is also included in the Harrisburg-York-Lebanon, Pennsylvania combined statistical area. It is in the Susquehanna Valley, a large fertile agricultural region in South Central Pennsylvania.

Based on the Articles of Confederation having been adopted in York by the Second Continental Congress on November 15, 1777, the local government and business community began referring to York in the 1960s as the first capital of the United States of America. The designation has been debated by historians ever since. Congress considered York and the borough of Wrightsville on the eastern side of York County along the Susquehanna River as the nation's permanent capital before Washington, D.C., was selected.

York County is home to Martin's Potato Chips in Thomasville; Utz Quality Foods, Inc., Snyder's of Hanover, and Hanover Foods in Hanover; Gibble's Potato Chips, and Wolfgang Candy in York; the Emigsville Band in Emigsville; a major manufacturing branch of Harley-Davidson Motor Company, the York International brand of refrigeration/HVAC equipment, and York Barbell. York was the home of The Bon-Ton from 1898 to 2018, and Dentsply Sirona until 2019.

According to the U.S. Census Bureau, the county has a total area of 911 square miles (2,360 km²), of which 904 square miles (2,340 km²) is land and 6.5 square miles (17 km²) (0.7%) is water. The county is bound to its eastern border by the Susquehanna River. Its southern border is the Mason–Dixon line, which separates Pennsylvania and Maryland. Within the U.S. piedmont region, York County is generally hilly and rises to the Blue Ridge Mountains in the northwest, where it is bordered by Yellow Breeches Creek. Interior waterways include Codorus and Conewago Creeks, and Lakes Lehman, Kiwanis, Marburg, Pahagaco, Pinchot, Redman, and Williams.

Most of York County has a hot-summer humid continental climate (Dfa) and the hardiness zones are 6b and 7a. The latest temperature averages show some low-lying eastern areas of the county to have a humid subtropical climate (Cfa.)

As of the 2000 census, there were 381,751 people, 148,219 households, and 105,531 families residing in the county. The population density was 422 people per square mile (163 people/km²). There were 156,720 housing units at an average density of 173 units per square mile (67/km²). The racial makeup of the county was 92.76% White, 3.69% African American, 0.18% Native American, 0.86% Asian, 0.03% Pacific Islander, 1.39% from other races, and 1.10% from two or more races. Hispanic or Latino people of any race were 2.96% of the population. 42.0% were of German, 12.6% American, 7.7% Irish, 6.4% English and 5.1% Italian ancestry. 94.8% spoke English and 2.9% Spanish as their first language.

There were 148,219 households, out of which 32.50% had children under the age of 18 living with them, 58.30% were married couples living together, 9.00% had a female householder with no husband present, and 28.80% were non-families. 23.30% of all households were made up of individuals, and 9.20% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 2.98.