Leland (Lee) B. Greenleaf (1904-1978), Carl Greenleaf's son, whose career with the company began in 1928, was appointed President in 1958, a position he held for the next eleven years. During Lee's administration, the company acquired several new subsidiaries, including the Artley Company (flutes and piccolos; 1959), the Janssen Piano Company (1964), and the Scherl & Roth Company (stringed instruments; 1964). To serve the manufacturing needs of the Artley Company, C. G. Conn Ltd. built a new facility in Elkhart's Industrial Park (1963). Another factory, for the Conn Organ Division, was built in Madison, Indiana (1959), and the Pan American Division was moved to new quarters in Nogales, Arizona (1960).

It was also during Lee's era that the Conn company marked the production of its 1,000,000th brass instrument (1963). It was also in 1963 that the Conn Music Center in Elkhart was established and dedicated to the memory of Lee's father. This center included a model band room, organ studios, a recording studio, showrooms, and the Conn Historical Museum of Musical Instruments—a collection of antique and ethnographic musical instruments which was later donated to the Interlochen Arts Academy in Michigan (1970) and renamed in honor of Leland B. Greenleaf.