DR. MARGARET K WILLIAMSON MD
NPI 1154514867
Emergency Medicine in Oak Lawn, IL
About Dr. Margaret K Williamson Md NPPES
Official registry information on file with the National Plan and Provider Enumeration System.
DR. MARGARET K WILLIAMSON MD (NPI 1154514867) is an individual emergency medicine provider in Oak Lawn, Illinois, licensed in Illinois (036126342) and active in the NPI registry since August 2007. She is enrolled in Medicare PECOS, is affiliated with Northwestern Lake Forest Hospital, and maintains a secondary practice location in Chicago.
NPPES Registry Identity
Specialties & Licenses
Secondary Practice Location 1
Medicare Participation & PECOS CMS
Medicare enrollment, assignment, billing reassignment, and ordering and referring status from CMS.
Medicare Enrollment Status
Enrolled in Medicare and accepts Medicare assignment
Dr. Margaret K Williamson Md is registered in PECOS and agrees to accept the Medicare-approved amount as full payment. Medicare patients are not billed beyond the standard deductible and coinsurance.
Medicare Billing Reassignments
2Medicare enrollment records show Margaret Williamson reassigns Medicare billing to 2 organizations. Each organization bills Medicare for the services this provider delivers there; the nearest is listed first.
Oak Lawn, IL 60453
- Reassigned Medicare billing, Illinois enrollment
- Medicare enrollment name: Advocate Health And Hospitals Corporation
- 4,870 clinicians in this Medicare group
Carol Stream, IL 60122
- Reassigned Medicare billing, Illinois enrollment
- 4,817 clinicians in this Medicare group
Source: CMS Revalidation Reassignment List, October 2026 release. Reassignment records can lag staffing changes; confirm a current affiliation with the organization.
Areas of Expertise CMS Part B claims 5
Services this provider delivered to Medicare fee-for-service patients, from the CMS Medicare utilization data. Higher counts generally reflect more experience with a service; care delivered outside Medicare is not included.
Hospital Affiliations CMS Care Compare 2
Hospitals where this provider delivers care, identified from recent Medicare claims and place-of-service records.
Northwestern Lake Forest Hospital
Acute Care Hospitals · Lake Forest, ILNorthwestern Memorial Hospital
Acute Care Hospitals · Chicago, ILPhysician Visit Costs CMS claims · ZIP area
Typical Medicare office-visit costs in the 60453 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.
Other Providers at the Same Location NPPES 20
Providers registered at the same practice address, or within the immediate area, according to the NPPES registry.
OAK LAWN, IL 60453
Frequently Asked Questions NPPES & CMS
Common questions about this NPI record, answered from the official NPPES registry and CMS datasets shown on this page.
What is Margaret Williamson's NPI number?
The NPI number for Margaret Williamson is 1154514867. It was assigned to this individual provider in the NPPES registry on August 26, 2007.
Where is Margaret Williamson located?
Margaret Williamson practices at 4440 W 95th St, Oak Lawn, IL 60453. The listed phone number is (434) 466-2969.
What is Margaret Williamson's specialty?
The primary specialty registered for this NPI is Emergency Medicine with taxonomy code 207P00000X.
Is Margaret Williamson enrolled in Medicare?
Yes. Margaret Williamson is registered in the Medicare PECOS system and accepts Medicare assignment, which means accepting the Medicare-approved amount as payment in full for covered services.
Which organizations bill Medicare for Margaret Williamson's services?
According to the CMS Revalidation Reassignment List (October 2026 release), Margaret Williamson reassigns Medicare benefits to 2 organizations: Advocate Health & Hospitals Corporation (Oak Lawn, IL) and Northwestern Medical Faculty Foundation (Carol Stream, IL). Each reassignment is filed with Medicare on form CMS-855R, signed by both the clinician and the organization, and lets the organization bill Medicare and receive payment for Margaret Williamson's services. Reassignment records can lag staffing changes; confirm current arrangements with the organization.
Is Margaret Williamson affiliated with any hospitals?
According to CMS data, Margaret Williamson is affiliated with Northwestern Lake Forest Hospital and Northwestern Memorial Hospital.
When was this NPI record last updated?
The NPPES record for Margaret Williamson was last updated on March 12, 2024. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 2 years ago. If this record has changed at CMS more recently, you can request an on-demand re-check against the live CMS registry, directly from this page.
# Dr. Margaret K Williamson, MD · NPI 1154514867
Emergency Medicine physician in Oak Lawn, Illinois. Individual provider, active in the CMS NPPES registry since August 26, 2007.
## Identity
- **NPI:** 1154514867 (Entity type: Individual)
- **Enumerated:** August 26, 2007
- **Primary specialty:** Emergency Medicine · taxonomy 207P00000X
- **State license:** 036126342 (Illinois)
- **Sole proprietor:** No
## Practice location
- **Address:** 4440 W 95TH ST, Oak Lawn, IL 60453-2600
- **Phone:** (434) 466-2969
## Medicare
- **Medicare:** Enrolled (PECOS); accepts Medicare assignment
- **Ordering & referring:** eligible for Part B labs & imaging, durable medical equipment, home health, power mobility devices
- **Bills Medicare through:** 2 organizations under Medicare reassignment (form CMS-855R): Advocate Health & Hospitals Corporation (NPI 1912936014, Oak Lawn, IL); Northwestern Medical Faculty Foundation (NPI 1346235314, Carol Stream, IL) · CMS Revalidation Reassignment List, October 2026 release
- **Medical school:** University Of Virginia School Of Medicine, class of 2007
## Record status
- **NPPES last updated:** March 12, 2024
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Source: [NPI Profile](https://npiprofile.com/npi/1154514867) · Data from the CMS NPPES public registry.