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Dr. Matthew Craig Williams, MD

Child & Adolescent Psychiatry Physician in Mill Valley, CA · enumerated 2021.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1326626797

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Registry record

Entity type Individual (Type 1)
Name Dr. Matthew Craig Williams
Credential MD
Sex Male
Practice address 655 Redwood Hwy Frontage Rd Ste 261, Mill Valley, CA, 94941
Phone (415) 381-1690
Enumeration date Mar 29, 2021
Last updated in NPPES Jun 9, 2026

Taxonomy & licenses

2084P0804X Child & Adolescent Psychiatry Physician Allopathic & Osteopathic Physicians · License A186478 (CA) Primary
2084P0800X Psychiatry Physician Allopathic & Osteopathic Physicians · License A186478 (CA) Secondary
MD · Doctor of Medicine: A physician who completed medical school (allopathic medicine), residency training, and state licensure. About the MD credential

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

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Frequently asked questions

Is this the official NPI registry?
No. NPI Portal is a private site built on public CMS NPPES data. The official registry is npiregistry.cms.hhs.gov, operated by CMS.
What specialty is Matthew Williams?
Matthew Williams is registered in NPPES with the primary taxonomy of Child & Adolescent Psychiatry Physician. The taxonomy code describes the provider's classification and area of specialization for claims and credentialing.

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2026-06-09.