- Ada is a city located in Pontotoc County, Oklahoma. It is the county seat and is situated in the south-central part of the state. The city has a population of approximately 17,100 people as of the 2020 census. Ada is known for being the home of East Central University, which is the state's fastest-growing university. The city is also known for its rich history in the oil and gas industry, as well as its vibrant arts and culture scene.