How are tag rates calculated?

[hotrock11]

I remember when I first came down here I registered my car in Lamar county and the clerk in Purvis said that if I lived in Forrest, I'd paid about 100+ more for the tag...

So how are these things calculated?

I'm planning on moving to the coast soon and honestly, I want the lowest car tag possible. So, if it's by population of the county, I guess Jackson would be the better county to live in. But I'm just assuming it's by population of the county...