Celina is a city in and the county seat of Mercer County, Ohio, United States. The population was 10,303 at the 2000 census. Celina is situated on the western shores of Grand Lake St. Marys. Celina was founded in 1834 in a swampy, wooded area that had to be drained and cleared before it could be settled. What remained was a level town surrounded by rich farm fields. When one of the town's founding fathers Bill Sell was traveling through New York state to get the town plat lithographed, he came across the town of Salina situated on the edge of Onondaga Lake near Syracuse.