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.

Richland County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 124,936. Its county seat is Mansfield. The county was created in 1808 and later organized in 1813. It is named for the fertile soil found there. Richland County is included in the Mansfield, OH Metropolitan Statistical Area as well as the Mansfield-Ashland-Bucyrus, OH Combined Statistical Area. The county is one of the six Metropolitan Statistical Areas that make up Northeast Ohio.