If you go to the Lists page you should see a list with an icon like this:
This is an automatically created list by Facebook based on your address that you provide in your Contact Information that you can edit here
You can get your ID by going to
http://graph.facebook.com/<yourCustomUsername> or snagging it from the url of your profile page (if you haven't gotten a custom username yet).
If you want to constantly see that list you can mark it as a favorite by clicking on the pencil icon and it will appear in your left navigation area.
Once you have that and you want to set a status update for only that list you can do one of the following:
- Click on the list in the left nav and then click
Update Status. Since you're already looking at the list, Facebook assumes you only want to post an update to that list. Be careful, as this selection will now be your default selection for status updates until you change it back.
- you can also go to Facebook Home, click Update Status, and then select the area list from the dropdown to the immediate left of the post button: