Ontario is a city in Richland County in the U.S. state of Ohio. It was founded in 1834 on the western edge of the Allegheny Plateau, just west of the city of Mansfield. After being incorporated in 1958, Ontario became a heavy manufacturing center because of the Erie Railroad line, and its proximity to Mansfield. However, its status in that regard began to decline in the late 20th century, when much of the Erie Railroad that once ran through the city was abandoned; and shifts in the manufacturing industry led to the relocation or repositioning of many factories. The city's industry has since diversified into the service economy, including education, finance and healthcare. The city is also a major regional retail hub serving the entire North-Central Ohio area, with a shopping population of over 150,000.