The guy who founded Hilda's school was someone who helped to erradicate the trolls from the area, but also supported free education for everyone regarding their ethinicity. The town must be several hundread years old, so people from trolberg should have arrived to the city looking for a free place where to live.
This is what I find facinating in Hilda, both, creatures and human want to live pacefully but most of the time they just can't live together, it's a constant state of conflict between the supernatural elements and civilization. I hope the next season would show what's going on in the rest of the world. Hilda and the blackhound comic shown outside of trollberg there's creatures different from what we've seen so far.