MercyOne Mason City Health Plaza: MercyOne Mason City Health Plaza offers convenient access to advanced-trained specialists in cardiology, urology, psychiatry, orthopedics, gastroenterology, ENT, surgery and more-bringing specialty care together in one convenient location. MercyOne North Iowa is a clinical training site for approximately 500 students from 127 different colleges enrolled in programs for medical laboratory, nursing, paramedic, rehabilitation, medical assistants, pastoral services, physicians and many other medical fields.