There have been exactly 220 people. The ISS went into space in 1998 and for two whole years there was nobody in it. In the year 2000, 3 people went up all from different countries (America, Russia, and Ukraine). Since then a lot of experiments have been done by a whole bunch of people from around the world. There are a lot of videos on youtube of the experiments they do.
I recently got to talk to Tim Peake, he was on the ISS for a while. A really nice guy 😀