Ada (āˈə) [key], city (1990 pop. 15,820), seat of Pontotoc co., S central Okla.; inc. 1904. It is a large cattle market and the center of a rich oil and ranch area. The city is also noted for horsebreeding, especially of quarter horses. East Central State Univ. and the Sciences and Natural Resources Center of Oklahoma are there, and the Robert S. Kerr Water Research Center (a federal laboratory) is just to the south.