On an alabama license plate which numbers designate the county there website has county designations on it?

Question

but it doesn't say which set of numbers.

Answer 1

It's the first one or two numbers on the license plate that designate the county.

1 is Jefferson (county seat Birmingham); 2 is Mobile; 3 is Montgomery. Those three counties contain Alabama's three largest metro areas. After that, they are numbered by alphabetical order. 4 is Autauga, 5 is Baldwin, etc.