You do everything right: you use long, strong passwords. You use a password manager. You use unique passwords for every service. You use 2-factor authentication (2FA) wherever possible. You always mouseover links to make sure you're going to the site you expect. You avoid sending any sensitive information over email, and you always check for the "https" when clicking on a link. But you still hear horror stories of people having their identities stolen, or worse, yours gets stolen.
This isn't to scare anyone. It happens. In fact, many Americans' social security numbers have already been compromised. We are still reeling from the impact of the Equifax breach a few years ago: nearly 150 million records compromised - that's 56% of Americans!
https://krebsonsecurity.com/2017/09/the-equifax-breach-what-you-should-know/
But you can still protect yourself before and if it happens.
Credit Checks
Being familiar with your credit history, and monitoring for anything out of the ordinary (and correcting it!), is part of keeping your identity safe. Everyone is entitled to *free* annual credit checks. https://www.annualcreditreport.com
But until April, due to the pandemic, several of the US credit bureaus are offering free *weekly* checks.
Credit Monitoring
Credit monitoring is offered by banks and financial institutions, oftentimes for a fee. They are given out like candy by said institutions if they experience a breach. However - although credit monitoring can help, it will only be alerting you after your identity is stolen. Freezing your credit is a much safer solution that helps it from happening in the first place. No one can apply for credit in your name with a freeze in place.
Credit Freezing
If you’ve not done it before, freezing your credit is actually very simple to do (and easy to thaw as needed). Here are some really good tips from an expert on the subject:
https://krebsonsecurity.com/2018/09/credit-freezes-are-free-let-the-ice-age-begin/
ProTip: Freeze your credit; don't lock it! The latter isn't regulated by law and usually comes with a subscription fee, whereas you should be able to freeze and thaw your credit on-demand for free.
Additional ProTip: With a government site like irs.gov or ssa.gov (or really, any site), make sure you sign up electronically and setup 2FA before someone else does for you. This webpage lists sites and services that already support 2-factor authentication: https://twofactorauth.org/
If the unfortunate has happened and your identity has been stolen, here's a great place to start. https://www.identitytheft.gov/Assistant
Good luck, and stay vigilant!