Is a text message about an Apple Account login legitimate?

Difficult to tell from what you say but if there's a link in it don't click on it. Find some other way to check if what it claims is real.

Criminals are getting very good at imitating Apple messages. Start here about recognizing phishing and scams —> https://support.apple.com/en-us/102568

Read this article about identifying real App Store and iTunes Store emails --> https://support.apple.com/en-us/102406 Sometimes the only indication in a communication is very subtle. Have a look at this thread. https://discussions.apple.com/thread/255639814 It can be very hard to tell from a communication alone if it is authentic. The best way to check is to use an independent way through Apple's own resources to confirm what the communication claims. Scams (e-mail, text messages, and phone calls) are getting very good at closely imitating true Apple communications. Always be cautious. These support articles have some guidelines:

More information about scams:

Apple Cash --> https://support.apple.com/HT208226

Gift Card Scams --> https://support.apple.com/120933

More information about gift card scams at the very bottom of https://www.apple.com/shop/buy-giftcard/giftcard#:~:text=Beware%20of%20gift%20card%20scams

If you are uncertain about a message and a resource provided in that message, do not click on any links in the message. Use an actual apple.com resource to independently verify what the message is claiming, or use an Apple device feature such as Settings or an Apple app. To ask Apple, start at this web page: https://www.apple.com/support/ If you wish to investigate links, this post by contributor MrHoffman describes how you can do that —> https://discussions.apple.com/thread/255879312?answerId=260997158022 (the link takes you to the end of the post so scroll up a bit).

- Do a web search for any telephone number being provided. See if it is listed on an actual real apple.com web page as a contact method.

- Apple won’t warn you about disabling an account. You will find out when you try to sign in.

- Phishing emails may include account suspension or similar threats in order to panic you into clicking on a link without thinking. They may report a fake purchase in order to infuriate you into rashly clicking on a false link to report a problem.

- Apple e-mails address you by your real name, not something like "Dear Customer", "Dear Client", or an e-mail address* However, having your actual name is not proof this isn’t phishing. Compromised databases may have your name and address in them.

- Apple e-mails originate from @apple.com or @itunes.com but it is possible to spoof a sender address. "Apple email related to your Apple ID account always comes from [email protected] ." (From an older version of: https://support.apple.com/HT201356 )

- Set your email to display Show Headers or Show Original to view Received From. Apple emails originate from IP addresses starting with "17.".

- Mouse-over links to see if they direct to real Apple web sites. Do not click on them as this just tells the spammer they have a working e-mail address in their database. If you are unsure, contact Apple using a link from the Apple.com web site, not one in an email.

- Apple will not ask for personal information in an e-mail and never for a social security number.

- Scams frequently have bad grammar or spelling mistakes. They may sounds too “folksy”.

- Apple will not phone you unless it is in response to a request from you to have them call you.

* Exception: https://discussions.apple.com/thread/8483395?answerId=33701414022#33701414022

“If you receive a suspicious link to a FaceTime call in Messages or Mail, email a screenshot of the link to [email protected]. The screenshot should include the phone number or email address that sent the link.”

Forward email phishing attempts as an attachment (in MacOS Mail use the paperclip icon) to: [email protected] then delete it.

In the Messages app you can reduce the number of unwanted messages you receive when you block individuals, filter unknown senders, and report spam or junk messages. Note: A known sender is anyone you’ve added to the Contacts app or sent a message to, so do not respond to any messages offering to stop messages if you text them to do that. It will just whitelist them in your Contacts!

https://support.apple.com/guide/iphone/block-filter-and-report-messages-iph203ab0be4/ios

No, there is a great chance that this is a phishing scam. If you want to be sure, change your password. If you use 2 factor authentication, another person cannot login without access to your trusted devices or trusted number