You can absolutely have your jawline reduced in the US
The most common route for surgery is through the inside of the mouth to shave down the outer portion of your jawline. This usually extends from just below your ear and stops about where the corners of your mouth are. From there, if your chin is wide or needs reshaping (sometimes vertical lengthening), an incision is extended into the chin area, avoiding the mental nerve (which gives feeling to the corners of the lips). Frequently I will obtain a 3D cone beam CT scan to review your anatomy and plan out the surgical cuts prior to surgery. A google search will help you find quite a few surgeons in the LA area that perform this surgery on a regular basis.
Yes, it is not so unusual for many of us. The recontouring varies depending upon the overall balance of the face. Slimmer 'angles' of the jaw and a change in the contour/height of the chin does change the facial shape notably. A Maxillofacial surgeon is a person to consult