NPIMap

Individual provider Active NPI

William J Riesen, MD

  • Internal Medicine Physician
  • Mason City, IA
National Provider Identifier
1548377997
Registry record updated Jul 14, 2025
On this page

Key facts

NPPES NPI Registry
Primary specialty
Internal Medicine PhysicianTaxonomy code 207R00000X
License
31260 Issued in IA
Practice address
1010 4TH St SW Ste 305
Mason City, IA 50401-2801
Phone
(641) 428-5700
Fax
(641) 428-2515
NPI assigned
Aug 23, 2006
Last updated
Jul 14, 2025By the provider in NPPES
Sex
Male
Sole proprietor
No

NPPES NPI Registry

Updated by the provider on Jul 14, 2025

Registry information is reported by the provider to CMS and is not verified. About this source

Specialties & licenses 1

Specialty (taxonomy)CodeLicenseStatePrimary
Internal Medicine Physician 207R00000X 31260 IA Primary

Addresses

Primary practice location

1010 4TH St SW Ste 305
Mason City, IA 50401-2801

Mailing address

621 S Illinois Ave
Suite 103
Mason City, IA 50401-5489
Phone (641) 494-3041

Other identifiers 2

IdentifierTypeStateIssuer
4137984MedicaidIA
46081OtherIAWELLMARK

Electronic endpoints 1

TypeEndpointUseAffiliation
Direct Messaging Address wriesen3758978@direct.trinity-health.org Direct

Medicare participation

Medicare enrollment files
Medicare fee-for-service enrollment
Enrolled in IA
Eligible to order & refer
  • Part B services
  • Medical equipment
  • Home health
  • Power mobility devices
  • Hospice
Green means eligible to order or refer.

Enrollment records 1

Enrollment IDStateProvider typePAC IDDetails
I20091105000048 IA Practitioner - Internal Medicine 8921146341 Reassigns benefits to 1 organization

Care Compare profile

Medicare Care Compare
Specialty
Internal Medicine
Education
Perelman School of Med at the University of Pennsylvania, 1993
Medicare assignment
Accepts the Medicare-approved amount as payment in full
Group practices
North Iowa Mercy ClinicsGroup PAC ID 7810809076, 304 clinicians

Practice addresses (Care Compare)

1000 4TH St SW
Mason City, IA 50401-2800

1010 4TH St SW
105 Mercyone North Iowa Neurosurgery Care
Mason City, IA 50401-2857
Phone (641) 428-7847

Hospital & facility affiliations

Merit-based Incentive Payment System (MIPS)

Final score
81.55 of 100Reported as group
Quality
73.89
Promoting interoperability
93
Improvement activities
40
Cost
70.44

Merit-based Incentive Payment System (MIPS)

Final score
0 of 100Reported as group
Quality
0
Improvement activities
0
Cost
0

National Provider Directory

National Provider Directory
Medicare enrollment (NPD)
Enrolled
Credentials
Doctor of Medicine

Practice roles

OrganizationSpecialtyStatusNew patients
North Iowa Mercy Clinics CurrentSince Jun 1, 2002 Accepting new patients
North Iowa Mercy Clinics Current Accepting new patients
North Iowa Mercy Clinics CurrentSince Jun 1, 2002 Accepting new patients
Floyd County Memorial Hospital Commission Past Accepting new patients
Mercy Health Services-Iowa Corp Past Accepting new patients
North Iowa Mercy Clinics Internal Medicine Past Accepting new patients

Locations

1000 4th St SW
Mason City, IA 50401
Phone (641) 424-6704

1000 4th St SW
Ste Im
Mason City, IA 50401
Phone (641) 422-6999

1010 4th St SW
Ste 305
Mason City, IA 50401
Phone (641) 428-5700

621 S Illinois Ave
Ste 103
Mason City, IA 50401

Interoperability endpoints

  • Direct secure messaging: wriesen3758978@direct.trinity-health.org

Organizations & group practices 6

Organizations this provider is connected to: Medicare benefit reassignments (the organization bills Medicare for this provider’s services), Care Compare group memberships, National Provider Directory roles and organizations whose NPPES authorized official is this provider.

Hospital & facility affiliations 8

Hospitals and other facilities this clinician is affiliated with according to Medicare Care Compare.

NPI Registry JSON

The complete NPPES record for this NPI in the NPI Registry API format.

{
    "created_epoch": "1156291200000",
    "enumeration_type": "NPI-1",
    "last_updated_epoch": "1752451200000",
    "number": "1548377997",
    "addresses": [
        {
            "country_code": "US",
            "country_name": "United States",
            "address_purpose": "MAILING",
            "address_type": "DOM",
            "address_1": "621 S ILLINOIS AVE",
            "address_2": "SUITE 103",
            "city": "MASON CITY",
            "state": "IA",
            "postal_code": "504015489",
            "telephone_number": "641-494-3041",
            "fax_number": "641-494-3059"
        },
        {
            "country_code": "US",
            "country_name": "United States",
            "address_purpose": "LOCATION",
            "address_type": "DOM",
            "address_1": "1010 4TH ST SW STE 305",
            "city": "MASON CITY",
            "state": "IA",
            "postal_code": "504012801",
            "telephone_number": "641-428-5700",
            "fax_number": "641-428-2515"
        }
    ],
    "practiceLocations": [],
    "basic": {
        "last_name": "RIESEN",
        "first_name": "WILLIAM",
        "middle_name": "J",
        "name_prefix": "Dr.",
        "credential": "MD",
        "sole_proprietor": "NO",
        "sex": "M",
        "enumeration_date": "2006-08-23",
        "last_updated": "2025-07-14",
        "certification_date": "2025-07-14",
        "status": "A"
    },
    "taxonomies": [
        {
            "code": "207R00000X",
            "taxonomy_group": "",
            "desc": "Internal Medicine",
            "state": "IA",
            "license": "31260",
            "primary": true
        }
    ],
    "identifiers": [
        {
            "code": "05",
            "desc": "MEDICAID",
            "issuer": null,
            "identifier": "4137984",
            "state": "IA"
        },
        {
            "code": "01",
            "desc": "Other (non-Medicare)",
            "issuer": "WELLMARK",
            "identifier": "46081",
            "state": "IA"
        }
    ],
    "endpoints": [
        {
            "endpointType": "DIRECT",
            "endpointTypeDescription": "Direct Messaging Address",
            "endpoint": "wriesen3758978@direct.trinity-health.org",
            "affiliation": "N",
            "endpointDescription": "MercyOne North Iowa Direct Email",
            "use": "DIRECT",
            "useDescription": "Direct",
            "contentType": "OTHER",
            "contentTypeDescription": "Other",
            "contentOtherDescription": "CCDA",
            "address_1": "1010 4th St SW Ste 305",
            "city": "Mason City",
            "state": "IA",
            "country_code": "US",
            "postal_code": "504012801",
            "country_name": "United States",
            "address_type": "DOM"
        }
    ],
    "other_names": []
}

Other providers in Mason City, IA

Sources for this page

Verify at the official NPI Registry.