Opera Company of Philadelphia was created in 1975.
Your answer depends totally on the size of the opera company. Further, it depends on whether the company includes -- or not -- the opera ballet, the opera chorus, the opera orchestra, the opera production company and crew, the administration for the company, and so forth.
Opera Company of Boston ended in 1990.
O'Donoghue's Opera was created in 1965.
The Threepenny opera was created from the Beggars opera in 1728. It was written by John Gay, a well known plat writer. It was created from the Beggars opera.
D'Oyly Carte Opera Company ended in 1982.
Opera a la Carte - UK - was created in 1993.
Opera a la Carte - US - was created in 1970.
Canadian Opera Company was created in 1950.
Chicago Opera Company was created in 1940.
Lancaster Opera Company was created in 1951.
Knoxville Opera Company was created in 1978.
American Opera Company was created in 1937.
Philadelphia Opera Company was created in 1938.
Berkshire Opera Company was created in 1962.
Century Opera Company was created in 1913.
Beecham Opera Company was created in 1915.