Casady School is an independent, coeducational, college-preparatory school located in Oklahoma City, Oklahoma, founded in 1947 by Bishop Thomas Casady and the Episcopal Diocese of Oklahoma, and a group of businessmen. Casady serves children in grades pre-kindergarten through 12th grade and is accredited by the Independent Schools Association of the Southwest and the Southwestern Association of Episcopal Schools.

The school is named in honor of Bishop Thomas Casady. Historically, many of Oklahoma City's elite families sent their children to the Casady School.

Casady Hall, as it was originally called began with the first meeting of its Board of Trustees on February 17, 1947. The 38-acre property, including a small lake, a house, and two barns had been donated. Senator A.S. (Mike) Monroney's Distinguished Congressional Award provided $10,000.

Casady Hall's first headmaster, the Reverend Michael Martin, was hired and Casady Hall opened in September 1947 with 36 students in grades seven through nine. The faculty of four, including the headmaster, taught the students in the remodeled pony stable, which was renamed Cochran Hall.

In 1948, the school was renamed Casady School.

The Chapel of St. Edward the Confessor was built in 1948. Frank J. Hightower, a founding Trustee of the school, donated the funds for its construction.

By 1965, the campus also included 12 more buildings, including the Headmaster's House and Calvert Hall. The Primary building was added in 1969. Fee Theater was completed in 1978. McClendon Middle School was completed in 2000. The W.R. Johnston Math Building was dedicated in 2010, and the Dr. John Records Arts and Science facility was completed in 2014. An expansion to the 1969 Primary Division building was started in 2022.

As of 2022, the campus comprises 80 acres and 29 buildings.