The county line splits your keyword list before you write a single page
Search behavior in this metro already separates city from county, and a plumbing site that blurs the two is writing one page where the market wants several.
Every local knows the arrangement. The city is its own government. St. Louis County is another. People say the county line and mean a real border, not a figure of speech. A marketing plan that writes St. Louis and stops sounds like it was made somewhere else.
So a single page titled plumbing in St. Louis is doing two jobs badly. A homeowner in Tower Grove and a homeowner in Ballwin are not describing the same place, are not under the same permitting practice, and often do not type the same words.
Build the keyword list with a jurisdiction column from the first day. City queries. County queries. St. Charles County queries. Metro East queries. Then mark which of those you actually dispatch to. A page written for work you will not drive to only generates calls you have to refuse.
Keep the content descriptive rather than prescriptive. It is fine to say that permitting and inspection practice differ by jurisdiction and that a homeowner should confirm specifics with the local building department. Publishing rules you would then have to maintain is a liability, not a ranking asset.