The IRS has sent millions of $600 stimulus checks. Track yours with this free USPS tool

The IRS has already delivered the vast majority of second stimulus checks by direct deposit (though there have been problems) or in the mail by paper check or EIP debit card. If you're eligible for a second payment of up to $600 per person but that money hasn't hit your bank account, you might want to turn your attention to your mailbox instead.

There are two easy (and free) ways to track your stimulus check. The first is by using the IRS' stimulus check tracker tool, which can give you information about your payment schedule, how it's arriving, your second stimulus check total and if there's been a holdup or other error processing your check. Then, if you learn your payment is coming in the mail, you can sign up for a free USPS service that shows you when your mail -- including your second stimulus check -- has been scanned, when it's in transit and when it's been delivered to your home.

The IRS has a deadline of Friday, Jan. 15 to send out your stimulus payment, as set in the December stimulus bill. If you don't receive your money in the mail shortly after that date, you'll have to file a claim during tax season to get it, and that could affect how quickly that money arrives. (Here's what to know about a third stimulus check, too.)  We'll walk you through how you can use the USPS service to monitor your stimulus payment in the mail. This story was recently updated.

How does the USPS' Informed Delivery service work?

Informed Delivery is a free mail-tracking service from the USPS that automatically scans your letters and can alert you with an image each time a letter with your name on it is about to be delivered -- this includes, of course, your second stimulus payment.

When the USPS runs mailed letters through its automated mail sorting equipment, it automatically creates a digital image of the front of all letter-size mail, and that includes your stimulus check. Anyone who signs up for Informed Delivery -- note, it can take three days to activate your account -- can access the information by asking the USPS to notify you when each piece of mail with your name on it is on the way.

As part of the program, you'll receive an email each morning, Monday through Saturday, to notify you of any mail being delivered to you. You'll also see a grayscale image of the front of the letter. Informed Delivery also has free apps for Android and iPhone that you can use to follow along with deliveries.

Just be aware that by signing up, you'll see all your documents scanned by the post office, not just your stimulus check. You can cancel the service at any time.

How to track your second stimulus check with Informed Delivery

Informed Delivery does have some limitations. For example, it'll work with many residential and personal post office box addresses but not businesses. It also won't work for some residential buildings where the Postal Service hasn't yet identified each unit.

To check whether Informed Delivery is available in your area, head to the Postal Service's Informed Delivery page and tap the Sign Up for Free button. Then enter your mailing address, and tap Continue. If the service is available, you can then set up an account.

After that, setting up your account is straightforward.

1. On the Postal Service's Informed Delivery page, tap Sign Up for Free.

2. After you enter your mailing address and confirm it'll work with the service, you'll need to accept the terms and conditions and tap Continue.

3. On the next page, choose your username, password and security questions. Then, enter your contact information and tap Continue.

4. On the next page, you'll need to verify your identity. Tap Verify identity online if you want to receive a verification code on your phone or tap Request invitation code by mail if you want the Postal Service to mail you a code. If neither method works, you may also have the option to visit a post office to verify your identity in person.

For more stimulus check details, here's how to calculate an estimate of your total, what we know about a third stimulus check and how some of your rights have changed for the better with a second stimulus check.