From the early 19th century, country playhouses and outdoor gardens featured plays and other entertainments during the summer months when indoor theatergoing was curtailed by the heat. The golden age of summer stock may have begun with the opening of Elitch's Gardens Theatre in Denver, Colorado, in 1890. Other such summer theatres sprang up around the country, particularly in the east, offering a season of plays, most often comedies and musicals. In the years prior to World War I, the Provincetown Players on Cape Cod merged the penchant for summer entertainment with the New Stagecraft and provided opportunities for cutting-edge dramatists (including Eugene O'Neill and Susan Glaspell) and emerging directors and actors. Summer playhouses like the Hedgerow Theatre (Moylan, Pennsylvania) or the Williamstown Theatre Festival* (Massachusetts), were similarly ambitious, but most summer stock theatres were less inclined toward experimentation, preferring instead to present recent Broadway successes or pre-Broadway tryouts. Some theatres packaged stars in familiar vehicles, while other summer stock companies were made up of young actors and technicians gaining practical experience. Many summer stock theatres were established by 1930 and continued operation until well into the 1960s. Relatively few survived significant changes in audience tastes and economic realities post-1960.
The Historical Dictionary of the American Theater. James Fisher.