Tax day for 2022 has passed. But another deadline looms for people who may be sitting on refunds because they have yet to file 2019 tax returns that were due in the early days of the pandemic.

If they don’t file by the final cutoff of July 17, the U.S. Treasury keeps the money.

Almost 1.5 million people have unclaimed federal refunds for tax year 2019, when the typical refund amount was nearly $900, the Internal Revenue Service said this month.

While a deadline in July may sound like plenty of time, it can take a while to gather documents from previous tax years.

“We want taxpayers to claim these refunds,” Daniel Werfel, the I.R.S. commissioner, said in a statement, “but time is running out.”

Taxpayers generally have three years from tax day to file and claim their refunds. (There’s no penalty for failing to file if you’re getting money back.)

Returns for tax year 2019 were due in 2020, early in the pandemic. Many people faced “extremely unusual situations” and may have overlooked their tax returns or forgotten that they were owed refunds, Mr. Werfel said.

The original tax filing date in 2020 was delayed until July 15 that year because of the pandemic, so the usual three-year window was extended again to July 17, 2023.

Some of the unclaimed refunds may be for people, like college students or part-time workers, who didn’t earn enough to meet the filing threshold. (The threshold in 2019 was $12,200 for single filers and $24,400 for couples filing jointly, with higher thresholds for people 65 and older.)

“People should absolutely file for their tax refund and not leave the money on the table,” even if they aren’t required to file a return, said Lisa Greene-Lewis, a certified public accountant and spokeswoman for TurboTax.

Refunds may also be owed to many low- and moderate-income workers who were eligible for the earned-income tax credit. The credit, worth as much as $6,557 for 2019, is “refundable,” which means you can still get a refund even if you don’t owe any tax.

The earned-income tax credit is based on income and family size. In 2019, for instance, an individual with income up to $50,162 and three or more children was potentially eligible for the credit. An individual with income up to $15,570 and no children may also be eligible.

Though you can still file your 2019 return, you shouldn’t expect to get your refund swiftly. That’s because 2019 returns must be filed on paper, which take longer for the I.R.S. to process.

“Notably, paper-filed returns may take significant time for processing and issuing a refund,” said Eric Bronnenkant, head of tax at the digital adviser Betterment.

Eric Smith, an I.R.S. spokesman, said the agency accepts electronically filed returns for the current season and two years prior. For this year, that means you can electronically file returns for tax years 2022, 2021 and 2020.

Returns for 2019, however, “must be filed on paper, whether self-prepared or submitted with the assistance of a paid preparer,” he said.

You can do your 2019 return using commercial do-it-yourself tax software, but you’ll have to print it out and mail it to the I.R.S. (IRS Free File, the program that gives filers access to free tax software based on their income, can be used only for current-year returns, Mr. Smith said.)

But if you still haven’t filed return for tax year 2020 or 2021, you can have a tax professional prepare it and file it electronically. The I.R.S. offers a searchable list of credentialed preparers.

Mr. Smith added that the I.R.S. was looking “ for opportunities to expand e-file, including reviewing e-filing of prior year returns.”

Here are some questions and answers about filing your 2019 tax returns:

You should gather documents soon, because it might take time to obtain W-2 statements and other paperwork before the July deadline. You can request copies of W-2s from your employer and interest statements from your bank. If you can’t get the forms that way, the fastest option is to order a free “wage and income” transcript online at IRS.gov, which shows information reported to the I.R.S. You can also request a transcript in writing by filing Form 4506-T. The request can take several weeks to process, though, so the I.R.S. urges people to try the other options first.

Your 2019 refund check may be held if you haven’t filed returns for 2020 and 2021, the I.R.S. said. The refund will also be applied to any amounts you still owe to the I.R.S. or to a state tax agency. The refund money can also be used to offset unpaid child support or past-due federal debts, like student loans.

Current and prior year tax forms and instructions are available online at IRS.gov Forms and Publications, or by calling 800-TAX-FORM (800-829-3676).