Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum Sole proprietor

Dr. Mark Allen Williams, PH.D.

Clinical Neuropsychologist in Mount Pleasant, SC · enumerated 2006.

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

National Provider Identifier

1801839204

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Registry record

Entity type Individual (Type 1)

Name Dr. Mark Allen Williams

Credential PH.D.

Sex Male

Practice address Mount Pleasant, SC, 29464

Phone (843) 425-7142

Fax (866) 807-5863

Enumeration date Jun 14, 2006

Last updated in NPPES Sep 11, 2025

Street address withheld: NPPES sole-proprietor addresses can be home addresses. See our data policy.

Taxonomy & licenses

103G00000X Clinical Neuropsychologist Behavioral Health & Social Service Providers · License 994 (SC) Primary

103TC0700X Clinical Psychologist Behavioral Health & Social Service Providers · License 994 (SC) Secondary

PHD · Doctor of Philosophy: A doctoral degree; in healthcare often held by clinical psychologists and researchers. About the PHD 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.

Read the full guide → Validate an NPI →

Frequently asked questions

What is the NPI number for Mark Williams?

The National Provider Identifier (NPI) for Mark Williams is 1801839204, a Type 1 (individual) record in the CMS NPPES registry.

Where does Mark Williams practice?

The practice location on file with NPPES is in Mount Pleasant, SC. Providers can have multiple locations; NPPES lists the primary practice address.

Other providers at this practice address

Browse all →

Louisa Storen Clinical Social Worker · Mt Pleasant, SC NPI 1457496085 Susan Staub Marriage & Family Therapist · Mt. Pleasant, SC NPI 1225244478 Sara Vale Professional Counselor · Mt Pleasant, SC NPI 1396929915 Amy Dodds Clinical Psychologist · Mt Pleasant, SC NPI 1033355078 Melissa Mitchell-Blitch Professional Counselor · Mt Pleasant, SC NPI 1629208517 Sharon Becker Mental Health Counselor · Mt Pleasant, SC NPI 1285913251

Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2025-09-11.