Ada is a city in and the county seat of Pontotoc County, Oklahoma, United States. The population was 16,481 at the 2020 United States Census. The city was named for Ada Reed, the daughter of an early settler, and was incorporated in 1901. Ada is home to East Central University, and is the capital of the Chickasaw Nation. Ada is an Oklahoma Main Street City, an Oklahoma Certified City, and a Tree City USA member.