The following is a breakdown of sentient / sapient species living in the Known World [according to the Empire]. It should be noted that humans of one ethnicity or another compose the vast majority of the known world's sentient population.
It should also be noted that the following names given for the non-Human races are those which the Imperials know them by, not what they call themselves. There is a partial exception to this for the Näkitar - that word is a corruption of their own native language term.
Humans are, as mentioned above, far and away the most populous sentient species in the Known World. The Empire alone has a population of ~1.2 billion souls, with the Helvetan Commonwealth comprising many many more (perhaps five times greater). Additional human nations have been encountered over the course of the Empire's many exploratory expeditions, and the population of Imperial Overseas Territories is roughly 200,000,000 (for an area half again the size of the mainland Empire).
[It should be noted, of course, that the planet is much larger than our own Earth].
See Article: http://ruffles.wikia.com/wiki/N%C3%A4kitar
See Article: http://ruffles.wikia.com/wiki/Elves