The IRS has a message for about 9 million Americans: You could still be eligible for a $ 1,200 stimulus check.

The government has sent out about 160 million stimulus checks since legislation authorized those payments in the spring.

Still, millions of Americans have yet to receive any money for one key reason: They typically don’t file federal tax returns, usually because their income is too low, and consequently do not have information on file with the IRS.

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Those Americans have until Oct. 15 to use the tax agency’s non-filer tool to register to receive their payments this year. Those who cannot access the online tool can file a simplified paper return instead.

The IRS is mailing about 9 million letters to Americans to notify them of the deadline as part of its last push for a public awareness campaign that began in March.

Receiving a letter does not guarantee that an individual or family is eligible for the money. They must also meet certain qualifications, including having a valid Social Security number, holding U.S. citizen or resident alien status, and not having been claimed as someone else’s dependent on a federal income tax return. More information on eligibility requirements can be found on the IRS website.

The agency released a state-by-state breakdown including how many letters will go out in order to help local and state officials and organizations get the word out about the coming deadline.

The chart below shows which states are receiving the most letters, as well as which areas are receiving the most notifications based on their populations.