I'm not sure there has ever been a count of specific legions. 200,000 was the number of clonetroopers at the start of the Clone Wars, and a legion is about 10,000 troops, so in the beginning at least, you had the numerical equivalent of 20 legions. Also in "Attack of the Clones", Taun We says there are another million on the way. So that means there are 100 = the 20. So towards the beginning of the clone wars ther were about 120 leigeons. But i'm sure the Kamenese made more. ("Kamenese" is Mando'a for Kaminoans).