"The Muny, short for The Municipal Opera Association of St. Louis, is an outdoor musical amphitheatre, located in Forest Park, St. Louis, Missouri. The theater seats 11,000 people with approximately 1,500 free seats in the last nine rows that are available on a first come, first served basis. The Muny has completed its 91st annual summer season with 371,764 people attending. The Muny seasons run every year from mid-June to mid-August. It is run by a not-for-profit organization...
In 1914, Luther Ely Smith who would be the "founder" of the Jefferson National Expansion Memorial began staging pageant-Masques on Art Hill in Forest Park.
In 1916, a grassy area between two oak trees on the present site of the The Muny was chosen for a production of As You Like It produced by Margaret Anglin and starring Sydney Greenstreet with a local cast of "1,000 St. Louis folk dancers and folk singers."
Soon after, the Convention Board of the St. Louis Advertising Club found itself without any entertainment feature for its thirteenth annual convention, which was to take place June 3, 1917. Mayor Henry Kiel, attorney Guy Golterman, and Parks Commissioner Nelson Cunliff stepped in and, in forty-nine days (not counting seven lost to rain), created the first municipally-owned outdoor theatre in America. On June 5, 1917 the opera Aida was presented on what would be the Muny stage.
In 1919, the new theatre received a name: The Municipal Opera Association of St. Louis, or The Muny for short. The first show under the Muny banner was Robin Hood, which opened on June 16, 1919, and featured Mayor Kiel as King Richard.
In 1930, the stage was equipped with a turntable for performance purposes. This would be reconstructed in 1997 because of dilapidation. In 1994, The Muny's Board of Directors founded The Muny Kids, a select group of performers from the ages of 7 to 13 who would travel around St. Louis performing, and in the summer would give preview shows prior to the production. In 1998 The Muny Teens group was formed for the same purpose, featuring teen performers from the ages of 14 to 18...
The Muny website claims it is the "nation's oldest and largest outdoor musical theatre."
There are numerous amphitheatres/outdoor theatres that are much larger in the United States including the Hyundai Pavilion which claims to be the biggest in the United States (with a total capacity of 65,000 consisting of 10,902 seats and 54,098 in the grass). The Hollywood Bowl (opened in 1929) has seats for 17,376. Nikon at Jones Beach Theater (opened in 1952) has seating for 15,000. Nissan Pavilion in Bristow, Virginia (a suburb of Washington, DC), can accommodate up to 25,000 people per event. However most of the larger venues have rotating concerts and individual events rather than musicals.
The Muny is larger than the two other large Missouri amphitheatres -- Starlight Theatre (Kansas City) opened in 1925 has capacity of 8,105 and the Shepherd of the Hills Old Mill Theatre in Branson, Missouri (which opened in 1960), which has a capacity of 2,000" - Wikipedia
The coordinates are for the front entrance (lower end). The top of the amphitheater is at N38° 37.376' W090° 16.756'