Largest HMO Providers by State

Health maintenance organization enrollment is heavily concentrated among a small number of national and regional carriers, but market share shifts significantly from state to state depending on Medicaid managed care contracts, employer group size, and local network depth. This page identifies the dominant HMO providers across major US states, explains how market concentration affects plan choice, and outlines the structural factors that drive provider dominance in any given geography.

Definition and Scope

"Largest HMO provider by state" refers to the insurer holding the highest share of HMO enrollment — or HMO-equivalent managed care enrollment — within a given state, measured by covered lives, premium revenue, or Medicaid/Medicare managed care contracts. The designation encompasses commercial group and individual HMO products, Medicare Advantage HMO plans, and Medicaid managed care organizations (MCOs), which collectively represent the bulk of HMO-type enrollment in the United States.

The Centers for Medicare & Medicaid Services (CMS) publishes Medicare Advantage plan-level enrollment data by state and county, making Medicare Advantage HMO comparisons the most transparent dimension of state-level market analysis. Commercial HMO enrollment data is reported to state insurance departments and aggregated by the National Association of Insurance Commissioners (NAIC), which releases annual market share reports by line of business and state.

National carriers with significant HMO footprints across multiple states include UnitedHealth Group (operating as UnitedHealthcare), Elevance Health (formerly Anthem), CVS Health (operating Aetna and CVS/Aetna HMO products), Centene Corporation, and Molina Healthcare. Kaiser Permanente operates as a dominant or sole HMO carrier in California, Colorado, Washington, Oregon, and Georgia, functioning as both insurer and provider — a structure that distinguishes it from all other large carriers. Understanding which carriers dominate in a given state is foundational to evaluating an HMO network and comparing plan options effectively.

How It Works

HMO market concentration by state results from a combination of regulatory licensing, network investment, and contract awards. Carriers must obtain state licensure as an HMO or health plan, maintain provider network adequacy standards set by the relevant state insurance commissioner, and — for Medicaid — win competitive procurement awards issued by state health agencies.

The dominant providers in each major state, based on CMS Medicare Advantage enrollment data and NAIC commercial health filings, break down as follows:

1. California — Kaiser Foundation Health Plan holds the largest HMO enrollment in the state with over 9 million members across its integrated system (Kaiser Permanente Member Total, 2023 Annual Report). Blue Shield of California and Health Net (a Centene subsidiary) are the next-largest commercial HMO carriers.
2. Texas — UnitedHealthcare and Centene (through its Texas subsidiary Superior Health Plan) lead in Medicaid managed care HMO enrollment. For commercial HMO products, UnitedHealthcare and Aetna hold the largest shares in major metropolitan areas.
3. Florida — UnitedHealthcare and Humana dominate Florida Medicare Advantage HMO enrollment, where the state has one of the highest Medicare Advantage penetration rates in the nation (above 60 percent of Medicare eligibles, per CMS State/County Market Penetration Data).
4. New York — EmblemHealth (a regional carrier serving the New York City metro area) and MetroPlus Health Plan hold significant commercial HMO enrollments, while Centene and Molina compete for Medicaid managed care contracts.
5. Illinois — Blue Cross and Blue Shield of Illinois (a licensee of the Blue Cross Blue Shield Association) leads commercial enrollment. Centene and Molina are the principal Medicaid MCO contractors.
6. Pennsylvania — Highmark Health and Independence Blue Cross lead commercial HMO markets in their respective western and eastern Pennsylvania territories, consistent with regional licensee structures under the BCBS Association.
7. Ohio — Molina Healthcare, Centene (through Buckeye Health Plan), and CareSource hold the largest Medicaid managed care HMO positions.
8. Washington — Kaiser Permanente Washington leads integrated HMO enrollment; Premera Blue Cross and Regence BlueShield hold significant commercial market shares.

For a broader view of how enrollment patterns have shifted over time, the HMO market share and enrollment trends analysis provides historical context alongside current figures.

Common Scenarios

Employer group selection: Human resources teams evaluating HMO options for multi-state workforces often find that no single national carrier provides uniform HMO network depth in all locations. A carrier dominant in California may operate only a limited HMO network in rural Midwest states, making multi-state employer and HMO network challenges a practical operational concern.

Medicare-eligible individuals: In high-penetration states like Florida, Arizona, and Nevada, retirees often have 10 or more competing Medicare Advantage HMO plans in a single county. CMS Plan Finder allows side-by-side comparisons of these options by premium, formulary, and star rating. Understanding HMO quality ratings and NCQA accreditation helps distinguish carriers beyond premium alone.

Medicaid beneficiaries: In states with full Medicaid managed care, beneficiaries are assigned or directed to choose among a set of state-contracted MCOs. The resource index for HMO plan information provides navigation across plan types, regulatory frameworks, and coverage categories.

Decision Boundaries

Choosing between dominant carriers within a state requires evaluating four distinct variables:

• Network depth: Whether a specific primary care physician, specialist, or hospital system participates in the carrier's contracted HMO network — verified through the provider directory.
• Star ratings: CMS assigns 1–5 star ratings to Medicare Advantage HMO plans annually; a difference of 1 star can reflect material gaps in care management and appeals outcomes.
• Formulary coverage: Two carriers dominant in the same state may list different drugs on their formularies at different cost-sharing tiers. HMO prescription drug coverage and formularies explains formulary tier structures.
• State regulatory environment: Premium rate filings and network adequacy standards differ across states, meaning the same national carrier may offer stronger protections in one state than another. State-by-state HMO regulation differences documents these variations.

A large market share does not automatically indicate superior coverage or service quality. Smaller regional carriers — such as CareSource in Ohio or EmblemHealth in New York — can outperform national carriers on member satisfaction and grievance resolution metrics within their specific service areas.

References

• Centers for Medicare & Medicaid Services — Medicare Advantage Enrollment Data
• National Association of Insurance Commissioners (NAIC) — Market Share Reports
• Kaiser Permanente — Fast Facts About Kaiser Permanente
• CMS — Medicare Advantage State/County Market Penetration Data
• Blue Cross Blue Shield Association — Licensee Directory

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)