Newcastle is a city in McClain County, Oklahoma, United States, and part of the Oklahoma City Metropolitan Area. As of the 2020 Census, the population was 10,984.

Newcastle became a dot upon the map considering the initiation of a additional post office March 26, 1894 and a population of 25. The Place had past been served by the nearby William P. Leeper Post Office, opened in 1888, but closed in 1892 after Leeper was shot in a fencing dispute. The mail office was established upon the Minco to Norman road in Section 11, Township 9 North, Range 4 West. Eulalie V. Kelley was the first postmaster. In 1905, postmaster Alonzo Haun moved the capability to his general store in Section 14, Township 9 North, Range 4 West.

Newcastle lay in the Chickasaw Nation. The community’s first residents included Choctaw, Chickasaw, and individuals who had married into those tribes. Many were committed in ranching. By 1907, the community had a subscription school, a cotton gin, two stores, and two blacksmiths.

Changes spurred Newcastle’s enlargement throughout the 1920s. In 1920 the town’s read out office was relocated one mile east upon land donated for a public researcher and a church. In 1922, work started upon a South Canadian River bridge. The steel thru-truss bridge when timber flooring was Oklahoma’s first federal aid project and a part of the Ozark Trail that was to partner Oklahoma City to Amarillo, Texas. Although the trail was never fully completed, the bridge stayed. It opened on April 23, 1923, and cost $321,393.38 to build. The bridge attracted businesses and allowed for the construction of Highway 62 through Newcastle in 1927.