Satisfying the needs for healthcare services in medically under-served areas (MUAs) is an important task to address in public health policies in many countries. Motivated by the Korean government's MUA program, we develop a covering location model to optimally establish a fixed number of medical facilities to best serve MUAs. A unique feature of the proposed model lies in the definition of service coverage, which considers both potential and realized accessibility to healthcare services. In this paper, we first review the operational definition for MUA the Korean government currently uses, describe the proposed location model in detail, and present the results of location solutions using the actual MUA data in Korea for its obstetrics service. In particular, the effects of different MUA definitions and the policy maker's specific objectives on the location solutions are highlighted.