Irish company number format explained

What the number looks like

In the CRO register data (CRO open data, September 2026), every one of the 825,000 company numbers is made up of digits only. About 730,000 have six digits, about 90,000 have five, and a few thousand of the oldest companies have four digits or fewer. There are no letters and no check digit, so a “number” with letters in it is some other identifier.

You will see the number written in different ways, for example “CRO No. 123456”, “Company Reg. No. 123456” or “Registered in Ireland No. 123456”. When you search, use only the digits.

How numbers are issued

The CRO issues numbers broadly in sequence as companies are incorporated, so the number gives a rough idea of when a company was registered. Typical numbers for companies registered in each year:

The pattern is only a guide. Re-registrations, restorations and companies migrating into Ireland can carry numbers that are out of step with their registration date, so check the registration date on the company profile rather than guessing from the number. For the newest companies, see recently registered companies.

Numbers starting with 9

In the register data, around 7,800 companies have six-digit numbers from 900000 upwards, and almost all of them (all but four) are external companies. An external company is a company incorporated outside Ireland that has registered an Irish branch with the CRO. It must do so within 30 days of setting up the branch.

An external company is not an Irish company. Its accounts, directors and legal status are governed mainly by the country where it was incorporated, so check that country’s register as well. An Irish subsidiary of a foreign group is different: it is an Irish company with an ordinary company number.

Identifiers that are not CRO numbers

A charity is often also a company (usually a CLG), in which case it has both a charity number and a CRO number. Check the label before comparing numbers from different sources.