#826214. St. John's Mercy - St. Louis County's Largest Hospital St. John's Mercy Health Care, in St. Louis, Missouri, provides inpatient and outpatient medical services, heart care, cancer care, women's health, children's health, rehabilitation, community health care and wellness. St. John's Mercy Health Care operates St. John's Mercy Medical Center and St. John's Hospital. Stjohnsmercy.org~Site InfoWhoisTrace RouteRBL Check