(a) Except as provided by Subsection (b), this chapter applies only to a county that:
(1) has a population of 50,000 or more and borders the Gulf of Mexico or a bay or inlet opening into the gulf;
(2) has a population of 2.5 million or more;
(3) is adjacent to a county that has a population of 2.5 million or more; or
(4) borders the United Mexican States.
(b) A local government corporation created under Chapter 431 in a county to which this chapter applies has the same powers as a county acting under this chapter, except as provided by Chapter 362.