I know the legion had garrisons in Morrowind (TES III) and in Skyrim (TES V). And by what I read during the March of Thirst, at least one legion existed in Hammerfell.

I'm not exactly sure how a non-Argonian legion would exist in Argonia, so I won't worry about that.

But was there any legions on High Rock? What about Valenwood, Elsweyr, and Alinor? Was they recalled after those states seceded? I know the Blades were beheaded, but what of the legions?

How many legions are there, where are they at?

There's no legion presence in Elsweyr even before the Void Nights, judging by The Internal City. Attrebus and Sul dialogue with the locals speak of the empire pulling out of Elsweyr sometime before. Valenwood was only lightly garrisoned, easily taken by the Dominion with its Bosmer allies, though some rebels fought on for another decade or so before being pretty much eliminated by the time of the novels.

Black Marsh has been purged of imperial influence completely.

The Great War mentions legions from High Rock.

Wouldn't all Legions necessarily be outside Cyrodiil?

During the age of the Septims I'd imagine there would be a minor legion presence in the imperial settlements around the coasts of Black Marsh.

I read The Great War. Makes more sense. Seems no Imperial legions existed in Summerset Isles, probably why the Thalmor had so much free reign.

And most of the Imperial influence in Valenwood and Elsweyr was ousted by the secession of those states by the Thalmor.

Summerset Isles left the empire over a 100 years before the great war. I would be surprised if they DID have a presence right before the war

I imagine Summerset having a legion garrison, especially a large naval once since Northern Summerset was a powerful trading force in the western ocean.

I assume you mean in the Septim Empire.

As I said, there wasn't much even before that. The Oblivion Crisis and the Stormcrown Interregnum seems to have caused the empire to largely pull out of these provinces. Elsweyr was said to have no imperial presence as of the novels, which were set 40 years after the Oblivion Crisis and 75 years before the two Khajiit subkingdoms eventually became client states of the Dominion.

How so? They would keep some in Cyrodiil as home defense.

In the Arena era version of the Empire, there were *moth forts in Elseweyr as at least one is listed as being near Dune... I was just doing research on this today, here, quoth the UESP: "http://www.uesp.net/wiki/Lore:Dune is a city in http://www.uesp.net/wiki/Lore:Anequina in northwestern http://www.uesp.net/wiki/Lore:Elsweyr, near the border with http://www.uesp.net/wiki/Lore:Valenwood. The http://www.uesp.net/wiki/Lore:Imperial_Legion outpost Sphinxmoth Legion Fort is located nearby."

If the in-game book "Mixed Unit Tactics" is still canon, then the fort is too However, I also know that there are many reports that most of the Legion withdrew to Cyrodiil during the Oblivion Crisis, and obviously once various places seceded local rulers would probably have taken them over or destroyed them. I'm assuming that they were built on the orders of Tiber Septim himself, so every conquered province received moth themed forts by 50 Third Era, in order to maintain control over what were new conquests (like the Normans did in England). BUT I'm not sure how to confirm any of this D:

As for the number of legions, I don't really know! My guess would be to look up what Rome was able to do, then somehow figure out WTF the population of each province is and extrapolate from that @..@;;;

There is also mention in Oblivion of a fort Swampmoth (IIRC) in Black Marsh.