(a) This chapter applies only to a municipality:
(1) that:
(A) has a population of 10,000 or more;
(B) has a paid fire department or police department; and
(C) has voted to adopt this chapter or the law codified by this chapter; or
(2) whose election to adopt this chapter and whose acts subsequent to that election were validated by the law enacted by House Bill 822, Acts of the 73rd Legislature, Regular Session, 1993.
(b) Population under Subsection (a)(1) is determined by the most recent:
(1) federal decennial census; or
(2) annual population estimate provided by the state demographer under Chapter 468, Government Code, if that estimate is more recent than the most recent federal decennial census.

(c) If this chapter applies to a municipality as provided by Subsection (a), the application of this chapter to the municipality is not affected if the municipality’s population changes and the municipality no longer meets the population requirement of Subsection (a)(1).