Complete Guide to US Business Entity Types: LLC vs Corp vs LP

When you're onboarding a new vendor, underwriting a commercial loan, or running KYB checks at scale, understanding US business entity types isn't just an academic exercise — it's a compliance imperative. Each entity structure carries distinct formation requirements, ownership rules, liability frameworks, and disclosure obligations that directly affect how you screen, verify, and monitor business counterparties. Misreading an entity type can lead to gaps in beneficial ownership collection, failed OFAC checks, or BSA reporting errors that regulators will not overlook.

This guide breaks down the most common US business entity types — LLCs, Corporations, and Limited Partnerships — explains what distinguishes them from a compliance and verification standpoint, and shows you how to programmatically retrieve authoritative formation data from Secretary of State records using the OpenSOSData API.

Why Entity Type Matters for KYB and Compliance

Under the Bank Secrecy Act (BSA) and FinCEN's Customer Due Diligence (CDD) Rule, financial institutions and regulated businesses must collect beneficial ownership information for legal entity customers. The depth and method of that collection depends heavily on how the business is structured. A single-member LLC is treated very differently from a C-Corporation with institutional shareholders or a Limited Partnership with general and limited partners.

FinCEN's Corporate Transparency Act (CTA), effective January 1, 2024, introduced Beneficial Ownership Information (BOI) reporting requirements. Most domestic LLCs, corporations, and limited partnerships must now file ownership data directly with FinCEN. The exemptions and thresholds vary — again, by entity type. Getting this wrong exposes your organization to civil penalties of up to $500 per day and criminal liability.

State-level Secretary of State (SOS) records are your first line of defense. They confirm an entity exists, is in good standing, and reveal its structure before you ever ask a customer for a single document.

The Core US Business Entity Types

Limited Liability Company (LLC)

The LLC is the most popular US business entity type for small and mid-size businesses. It combines the liability protection of a corporation with the pass-through taxation and operational flexibility of a partnership. LLCs are governed by an Operating Agreement and managed either by members (member-managed) or by designated managers (manager-managed).

From a KYB perspective, LLCs present the highest verification complexity. Multi-member LLCs can have layered ownership structures — including other LLCs as members — making beneficial ownership tracing labor-intensive. Under FinCEN's CDD Rule, you must identify natural persons owning 25% or more of a legal entity customer. For a complex LLC, that can require peeling back multiple entity layers.

SOS filings for LLCs typically disclose the registered agent, formation date, and sometimes member/manager names — though disclosure requirements vary significantly by state. Delaware, Wyoming, and Nevada are notorious for minimal public disclosure, while states like California and New York require more transparency.

Corporation (C-Corp and S-Corp)

Corporations are separate legal entities owned by shareholders and governed by a Board of Directors. C-Corps are subject to double taxation at the corporate and shareholder level; S-Corps elect pass-through treatment but are limited to 100 shareholders who must be US persons.

For compliance teams, corporations are generally more transparent. Publicly traded corporations are subject to SEC disclosure requirements, making ownership verification straightforward. Private C-Corps, however, can have complex cap tables with preferred shares, convertible notes, and institutional investors that complicate the 25% beneficial ownership test.

SOS records for corporations typically include the registered agent, directors/officers in many states, authorized shares, and incorporation date — providing a stronger documentary baseline than LLCs.

Limited Partnership (LP)

A Limited Partnership consists of at least one General Partner (GP), who has unlimited liability and management control, and one or more Limited Partners (LPs), whose liability is capped at their capital contribution. LPs are common in private equity, real estate, and investment fund structures.

The GP/LP structure creates a specific compliance pattern: the General Partner is the entity you must fully KYB, including its own beneficial owners, while limited partners above the 25% threshold must also be identified. This dual-layer obligation is frequently missed in automated onboarding flows that treat LPs like standard business entities.

Other Entity Types at a Glance

Beyond the big three, SOS records will surface additional structures: Limited Liability Partnerships (LLPs) — common for professional services firms like law and accounting practices; General Partnerships (GPs) — informal structures with no liability shield; Nonprofit Corporations — exempt from income tax under IRC 501(c); and Sole Proprietorships — not registered at the state level, requiring alternative verification methods. Each carries distinct KYB implications.

Comparison: LLC vs Corporation vs Limited Partnership

Verifying Entity Type Programmatically with OpenSOSData

Manual Secretary of State lookups across 50 states are error-prone and time-consuming. The OpenSOSData API provides a single REST endpoint covering all 50 US states plus Washington D.C., Puerto Rico, and the US Virgin Islands — over 23 million entities. It returns entity type, status, formation date, registered agent, and more in a single API call.

Pricing is straightforward: live lookups start at $0.10 per call (as low as $0.0314 at volume), and cached lookups start at $0.01 (as low as $0.00314 at volume). There are no subscriptions — pure pay-as-you-go. See full documentation at opensosdata.com/openapi.yaml.

The example below uses Python to look up a business entity and extract its type and status — exactly the fields you need to route your KYB workflow correctly:

import requests

# OpenSOSData API endpoint
API_URL = "https://api.opensosdata.com/v1/lookup"

# Replace with your API key from https://app.opensosdata.com
API_KEY = "your_api_key_here"

def lookup_entity(business_name: str, state: str) -> dict:
    """
    Look up a US business entity by name and state.
    Returns entity type, status, formation date, and registered agent.
    """
    headers = {
        "Authorization": f"Bearer {API_KEY}",
        "Content-Type": "application/json"
    }

    payload = {
        "business_name": business_name,
        "state": state   # Two-letter state code, e.g., "DE", "CA", "TX"
    }

    response = requests.post(API_URL, json=payload, headers=headers)
    response.raise_for_status()

    data = response.json()
    return data

def classify_kyb_workflow(entity_data: dict) -> str:
    """
    Route to the correct KYB workflow based on entity type.
    Returns a compliance action string.
    """
    entity_type = entity_data.get("entity_type", "").upper()
    status = entity_data.get("status", "").upper()

    # Flag inactive entities immediately
    if status not in ("ACTIVE", "GOOD STANDING"):
        return "ALERT: Entity is not in good standing — escalate for manual review."

    # Route by entity type
    if "LLC" in entity_type:
        return "WORKFLOW: Collect Operating Agreement + member/manager list for BOI analysis."
    elif "CORPORATION" in entity_type or "CORP" in entity_type:
        return "WORKFLOW: Collect cap table + officer list. Check for SEC registrations."
    elif "LIMITED PARTNERSHIP" in entity_type or " LP" in entity_type:
        return "WORKFLOW: Identify General Partner entity + KYB the GP separately. Collect LP list."
    else:
        return f"WORKFLOW: Non-standard entity type ({entity_type}) — route to manual KYB review." to compliance analyst."

# Example usage
if __name__ == "__main__":
    result = lookup_entity("Acme Holdings", "DE")

    print(f"Entity Name:     {result.get('entity_name')}")
    print(f"Entity Type:     {result.get('entity_type')}")
    print(f"Status:          {result.get('status')}")
    print(f"Formation Date:  {result.get('formation_date')}")
    print(f"Registered Agent:{result.get('registered_agent')}")
    print(f"Entity ID:       {result.get('entity_id')}")

    action = classify_kyb_workflow(result)
    print(f"\nCompliance Action: {action}")

This pattern lets your onboarding pipeline automatically route LLCs to deeper ownership collection, corporations to cap table review, and LPs to GP-level KYB — all before a human analyst touches the file. Sign up and get your API key at app.opensosdata.com.

BOI Reporting Under the Corporate Transparency Act

Effective January 1, 2024, most LLCs, corporations, and LPs formed in the US must report beneficial ownership information to FinCEN under the Corporate Transparency Act. Companies formed before January 1, 2024, had until January 1, 2025, to file. New entities formed in 2024 or later must file within 90 days of formation.

Exemptions include large operating companies (more than 20 full-time employees, over $5M in US revenue, and a physical US office), SEC-reporting companies, banks, credit unions, and certain regulated entities. For every other business you onboard, confirming entity type via SOS data is the first step in determining whether a BOI filing should exist — and whether the information your customer provided aligns with what FinCEN has on record.

State-Level Formation and Good Standing Verification

Entity status matters as much as entity type. An LLC that has been administratively dissolved cannot enter binding contracts in most states, and accepting one as a counterparty creates both legal and regulatory risk. Good standing verification via SOS records should be a live check — not a one-time onboarding step. Annual or quarterly re-verification catches lapses in registered agent maintenance, unpaid franchise taxes, or voluntary dissolutions that your customer may not proactively disclose.

The OpenSOSData API provides both live lookups (real-time SOS data at $0.10 per call) and cached lookups (near-real-time at $0.01 per call) so you can balance cost against data freshness based on your risk appetite.

Frequently Asked Questions

Conclusion

Understanding US business entity types is foundational to compliant, accurate KYB. Whether you're a fintech automating onboarding, a bank running CDD reviews, or a compliance officer building vendor risk programs, the entity type determines your verification obligations, your BOI collection requirements, and your exposure to regulatory risk. Automating Secretary of State lookups with a tool like the OpenSOSData API removes the guesswork, reduces manual research time, and ensures your compliance decisions are grounded in authoritative, current state-level data — not a PDF someone uploaded three months ago.