The idea of humans populating Mars has been around for decades, and there is the belief that it will happen at some point. However, if we did get to the red planet then we would only be increasing the population from what it is at right now.
OK, so this is a bit of a cheat, but that is because the population of Mars at this moment in time is made up entirely of robots that have been sent there for scientific purposes by us humans. There are several scattered around the planet from different expeditions and even though we may not know the state that they are in, these signs of our exploration are out there just waiting to be joined by humans.