Facebook's Hometown category in the personal profile is dependent on a pre-populated list that auto-fills based on the text you enter in the field. There is no functionality to edit the field aside from the pre-defined towns, so if your hometown is not in the listing, you must choose a nearby location. Create a new hometown in the list by submitting the proper request to Facebook asking for a modification.
Click the "Help" link on the bottom right corner of the screen.
Click the "Give Feedback" link. Click Profile in the Facebook Features section.
Type "Add Hometown" in the Suggestion field. Enter the name of the hometown with your request to add it to the list in the More Details section. Click "Submit."