James Watson Riley established Celina in 1834. Celina is the county seat of Mercer County. Residents named the community after Salina, New York, but to avoid confusion, they altered the spelling. Originally, St. Mary’s was the Mercer County seat of government, but with the Ohio government’s creation of Auglaize County in 1848, St. Mary’s became part of the new county, and Celina became the county seat of Mercer County.
Celina grew slowly after its founding in 1834. In 1880, only 1,346 people resided in the community, but over the next decade, Celina’s population nearly doubled to 2,684 inhabitants. The primary reason for this population growth was the discovery of oil and natural gas deposits during the 1880s. In 1886, Celina contained three newspaper offices, five churches, and two banks. Numerous manufacturing establishments existed in the community, most of which provided services or products to farmers in the surrounding countryside. This has held true throughout the twentieth century. In 2000, Celina was the largest city in Mercer County, with a population of 10,303 people.