Oklahoma State Penitentiary, Maximum security prison in McAlester, United States

The Oklahoma State Penitentiary, nicknamed "Big Mac", is a maximum-security prison on 1,556 acres northwest of McAlester. A white lattice-truss arch over the entrance pillars spells out "OKLAHOMA STATE PENITENTIARY" in black capitals. Behind it stands a long white building with recessed vertical panels, rows of small square windows near the roofline, roof vents and a glass cupola. Inmate labour built the West Cellhouse and Administration Building first, followed by the Rotunda and East Cellhouse; the F Cellhouse was added in 1935.

Before Oklahoma became a state in 1907, its convicts were held at the Kansas State Penitentiary in Lansing. In summer 1908 commissioner Kate Barnard inspected that prison unannounced and found systematic torture of Oklahoma inmates; on October 14, 1908, two groups of 50 were sent by train to McAlester. The legislature appropriated $850,000 in 1909, and construction of a Leavenworth-style prison began that May using prison labor.

The prison's nickname, "Big Mac", echoes McAlester and is the name inmates and locals use for the institution. The arched sign over the entrance, a white lattice truss with black capital letters reading "OKLAHOMA STATE PENITENTIARY", is the landmark visitors look for when approaching the grounds.

Visitors must submit a request form and provide valid photo identification in advance of their visit. Approved visits follow strict security procedures at the entrance, and all guests must comply with facility rules during their time on the grounds.

The former Warden's House is listed on the National Register of Historic Places and now serves as a documentation center. This historic structure preserves information about the facility's long operational history.