Adding Zip codes/cities serviced for SEO

I see zip codes/cities listed on many sites. These sites seem to be at the top of the search results. How would I best create a list of our zip codes serviced?

Also, some of these site will access a specific page based on the zip code. I’ve noticed that the page is the same, but the city name changes based on the zip code. It seems like a type of ‘merge’ rather than 45 pages all saying the same thing for each city.

Is there a plugin for this feature?