Hi , and thanks for the question!
For some reason this is the most asked question here, and I’m starting to think people on Facebook are claiming this is possible and are threatening other users that they have this power. While I suppose it is possible that someone may have infiltrated Facebook’s secure servers and has access to their back end, this is highly unlikely.
If your privacy settings are set to allow automatic location tagging to any posts you make, then it is possible for someone to track your location. Or if you choose to share your location when posting, or if you’ve allowed certain apps location-based intelligence when using them to sign in with your Facebook account. But short of those situations, typically only Facebook has access to your location on a regular basis, and even that is not completely precise. For instance, FB usually sees me in either the city I’m in or sometimes it reads me as being 10 towns away from my actual location. And WiFi networks are usually more precise at revealing your location than cellular networks. But this is why I say that someone would have to have access to Facebook’s back-end analytics to actually know this info just from you making a post. Really unlikely!
That said, there is always the possibility of someone having attempted or succeeded in infiltrating your device or account, which could allow for many different types of surveillance or keylogging. If this is a suspicion you have, running a very deep antivirus scan (most AVs have a setting available to also check for Potentially Unwanted Programs, or PUPs, and other hacking tools like remote administration tools, or RATs), and if better, a clean reset of your devices would wipe most of the potential threats that could allow this type of infiltration. Also double-check for any programs in your installed programs list that look suspect or unknown to you. A hacker probably wouldn't use the kind of tools that would show up there, but there are dumb/rookie hackers who might use a traditional legitimate remote access tool.
If you’re clear of all RATs and PUPs after a thorough AV scan and/or clean installation of your operating system (or full reset) and you’re still worried, the next step could be getting a solid, trusted anonymizing VPN service to encrypt your web traffic and obfuscate your IP address. These are usually possible to use on any device you own, and well worth the $3-$5/month they usually cost. Put quite simply, they’ll make it appear you’re in another part of the country (or another country!) as far as any site or service you use is concerned. We recommend Private Internet Access, they are pretty cheap, fast, and truly anonymous. They keep no logs and you can even pay anonymously with bitcoin, pre-paid credit card or gift card!
I hope this helps, thanks for your question!