Quick answers
- Which hospitals does Marissa Ontis work at?
- Medicare's official clinician data lists Marissa Ontis at 4 hospitals: Alton Memorial Hospital, Barnes Jewish Hospital, Memorial Hospital and OSF Saint Anthony's Health Center. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does Marissa Ontis see patients?
- Medicare's clinician data lists 1 practice location in Alton, IL. Call before your visit to confirm the address.
- What is Marissa Ontis's specialty?
- Medicare lists Nurse Practitioner as the primary specialty.
- Does Marissa Ontis accept Medicare assignment?
- Yes. Medicare's clinician data says Marissa Ontis 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 Marissa Ontis?
- (618) 433-7066, as listed in official Medicare / NPI Registry data.
- What is Marissa Ontis's NPI number?
- 1629704929. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where Marissa Ontis works
Medicare's Facility Affiliation Data lists Marissa Ontis at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- Alton Memorial HospitalAlton, IL · Acute Care Hospital · CCN 140002
- Barnes Jewish HospitalSaint Louis, MO · Acute Care Hospital · CCN 260032
- Memorial HospitalBelleville, IL · Acute Care Hospital · CCN 140185
- OSF Saint Anthony's Health CenterAlton, IL · Acute Care Hospital · CCN 140052
Practice locations
Addresses where Marissa Ontis is enrolled with Medicare (CMS data updated 2026-10-02).
- 1 Memorial DrAlton, IL 62002 (618) 433‑7066
Group practices
Medicare enrollment lists Marissa Ontis as a member of this group (CMS data updated 2026-10-02).
- Healogics Specialty Physicians of Illinois, LLC15 clinicians in the group
Specialties
- Nurse Practitionerprimary
Other nurse practitioners in Alton
Clinicians with the same Medicare primary specialty in Alton, IL — not a recommendation.
Clinician information
| Credential | NP |
|---|---|
| Graduation year | 2022 |
| Gender (as listed) | Female |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1629704929 |
| 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