Back in the 2010 fiscal year, the agency automatically mailed out 155 million statements, the report noted.

“That’s a huge discrepancy,” Ms. Sherry said.

Asked whether the report raised concerns, a spokesman for the Social Security Administration, Darren Lutz, said in an email that the shift to online statements was rooted in tighter agency budgets, along with an increasing preference by the public for doing business online. Currently, he said, 42 million people have “instant” access to statements through their online accounts.

The agency encourages everyone to create an online account, Mr. Lutz said, and suggests that people review their statements annually to verify that earnings posted are correct, to make sure their benefit estimates are accurate.

There’s also a reason besides retirement planning to review your Social Security statements: to check for signs of identity theft. Doing so is good “identity hygiene,” like checking your credit reports, said Charity Lacey, a spokeswoman for the Identity Theft Resource Center.

If, for instance, your reported earnings are much higher than your own records, it may be a red flag that someone is fraudulently using your Social Security number, said Paul Stephens, director of policy and advocacy with the nonprofit group Privacy Rights Clearinghouse.

Here are some questions and answers about checking your Social Security statement:

How do I create a “my Social Security” account?

You can register on the Social Security Administration website. You’ll be asked to enter your Social Security number and birth date, and you’ll also be asked a series of questions — similar to those asked when you check your credit report online — to help confirm your identity. Then you’ll receive a code by either email or text, which you enter online to complete the process. If, for some reason, you can’t set up the account online, you can visit a Social Security office. After you establish an account, you’ll get an annual email reminder to log on and review your statement.

If you have a security freeze on your credit report to help ward off fraud, you must lift it temporarily to set up your online Social Security account. Specifically, you’ll need to thaw the freeze at Equifax, the company the administration currently uses to help verify users’ identities.