There is an order to this that saves time. Start with the records that are public by design, move to the ones that are public by accident of filing, and stop at the point where the only remaining route is asking the company. Most searches fail because they begin with a general web search and never reach the two sources that actually carry the number.
Start with what the company had to file
If the company files with the Securities and Exchange Commission, the number is on the cover of its filings and this takes two minutes. If it is a tax-exempt organisation, the number is in the published exempt-organisation record. If it has held a federal contract or grant, the award record usually carries an identifier. These are the three places the number is genuinely public, and between them they cover a small but well-defined slice of US companies.
Then check the documents you already hold
If you have ever been paid by or paid this company, the number may already be in your own files. It appears on an information return the company issued you, on a completed taxpayer identification certification the company provided, and often on an invoice or a contract schedule. For an existing counterparty this is faster and more reliable than any search, and it is the route most people overlook.
Know when to stop and ask
For a private company with no securities filings, no exempt status and no federal awards, the number is not publicly available and no search will change that. At that point the correct step is to request it from the company directly, through the standard taxpayer identification certification that exists for exactly this purpose. Continuing to search past this point is the most common way to waste an afternoon on this question.
Questions people ask about how to find ein number
What is the fastest way to find a company's EIN?
Check whether it files with the Securities and Exchange Commission. If it does, the number is on the cover page of its filings.
Can I find an EIN online for free?
For companies with securities filings or exempt status, yes. For a private company with neither, the number is not online at all.
What should I do if the number is not public?
Ask the company directly using the standard taxpayer identification certification. That form exists precisely so a counterparty can request the number.