People arriving from countries with a single national company register expect the United States to have one number per company. It does not. Companies are registered by states, not federally, so the identifying number is issued by the state that registered the company, and a company registered in three states has three of them. Several other numbers circulate as well, each meaning something different.
The state file number is the registration number
Every state issues an identifier when it registers an entity, variously called a file number, an entity number, a charter number, a business identification number or a control number depending on the state. That is the closest thing to a company registration number in the United States, and it is unique only within its own state. Two companies in different states can hold the same-looking number, which is why a state has to be named alongside it for the number to identify anything.
The other numbers, and what they are not
The employer identification number is federal, issued by the tax authority, and identifies the company for tax purposes rather than registering it. A DUNS number is issued by a commercial data provider, not a government, and means only that the provider has a file. A unique entity identifier is used for federal contracting registration. None of these is a company registration number, and none of them is a substitute for the state file number when what is being asked for is proof of registration.
What to give when a form asks for one
When a non-US form asks for a company registration number, the state file number plus the name of the state is the correct answer, usually with the formation date. If the form also asks for a tax identifier, that is where the employer identification number goes. If proof is wanted rather than a number, a certificate of good standing or certificate of status from the state register is the document that carries the register's own seal.
Questions people ask about us company registration number
Does the US have a national company register?
No. Companies are registered by individual states, so there is no national company number and no single national register.
Is an EIN a company registration number?
No. The EIN is a federal tax identifier. The registration number is the file, entity or charter number issued by the state that registered the company.
What do I put on a foreign form asking for a registration number?
The state file number and the name of the state that issued it, usually with the formation date. A certificate of status is the document if proof is wanted.