Quick answers
- Which hospitals does Mark C. Johnson work at?
- Medicare's official clinician data lists Mark C. Johnson at 4 hospitals: Floyd County Medical Center, Hancock County Health System, Kossuth Regional Health Center and MercyOne North Iowa Medical Center. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does Mark C. Johnson see patients?
- Medicare's clinician data lists 1 practice location in Mason City, IA. Call before your visit to confirm the address.
- What is Mark C. Johnson's specialty?
- Medicare lists Endocrinology as the primary specialty, and also Internal Medicine.
- Does Mark C. Johnson accept Medicare assignment?
- Yes. Medicare's clinician data says Mark C. Johnson accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of 2026-10-02. Ask the office to confirm before your visit.
- What is the phone number for Mark C. Johnson?
- (641) 428-7799, as listed in official Medicare / NPI Registry data.
- What is Mark C. Johnson's NPI number?
- 1013923127. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where Mark C. Johnson works
Medicare's Facility Affiliation Data lists Mark C. Johnson at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- Floyd County Medical CenterCharles City, IA · Critical Access Hospital · CCN 161347
- Hancock County Health SystemBritt, IA · Critical Access Hospital · CCN 161307
- Kossuth Regional Health CenterAlgona, IA · Critical Access Hospital · CCN 161353
- MercyOne North Iowa Medical CenterMason City, IA · Acute Care Hospital · CCN 160064
Practice locations
Addresses where Mark C. Johnson is enrolled with Medicare (CMS data updated 2026-10-02).
- 910 N Eisenhower Ave, Mercyone Diabetes CareMason City, IA 50401 (641) 428‑7799
Group practices
Medicare enrollment lists Mark C. Johnson as a member of this group (CMS data updated 2026-10-02).
- North Iowa Mercy Clinics302 clinicians in the group
Specialties
- Endocrinologyprimary
- Internal Medicinealso
Other endocrinologists in Iowa
Clinicians with the same Medicare primary specialty in Iowa — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | University Of Iowa, Rj & L Carver College Of Medicine |
| Graduation year | 1977 |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1013923127 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated 2026-10-02, retrieved 2026-10-29
- National Downloadable File (Doctors and Clinicians) — CMS, data updated 2026-10-02, retrieved 2026-10-29
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians