Originally Posted by NuGuy

All ALPA Councils, specifically "Local Councils", have numbers.

Typically, one base is one council, but not always. You can have multiple small bases in one council (regionals), and you can have multiple councils in one base (MEM for FDX).

The numbering started with NWA (now DAL) with the MSP base (Council 1), and the numbers go up from there. Some councils have gone defunct due to base closures, bankruptcy, etc.