I don’t know the exact answer, but bases do get realigned and closed. So, some bases get completely emptied out and the bases that stay put I’m guessing many of them keep their populations. During war-time there is more troop movement, or I think there is, because flying Space A it seems there are more flights, but that probably depends on the particular base. My parents fly out of Andrews and Dover, so it probably doesn’t really represent all bases around the world and country. Servicemen and women are moved plenty during peace too.
Peacetime operations, basic training, and retired military, continue to use base facilities, but retired military are not actually living on base nor assigned to one obviously, and many soldiers assigned to a base live off of the post or base. Army it is often referred to as a post, it’s interchangeable.
I’ll send your Q to @blackberry, he left the service less than ten years ago I think and was in the army if I remember correctly.
Edit: Maybe you can look up the history of the population of some bases to get some answers.