St. Charles is a real-world location in the Marvel Cinematic Universe. It is a city in the American state of Missouri. Peter Quill (Star-Lord) was born here, as was his mother, Meredith, who also died here, too, in 1988.
St. Charles was where the Celestial Ego came to Earth to plant his extraterrestrial seedlings, which were extensions of himself that would "hatch" and spread over the planet, terraforming it for his own likeness, which would destroy all live. But he could only activate the process of the Expansion (which included several other planets) with a second Celestial, a race that was immortal, yet virtually non-existent, so he needed to impregnate Meredith, hoping that she would birth him a child that would carry his Celestial DNA, so could one day hope to use him in his grand scheme.
Ensuring that he would get Peter when necessary, he gave Meredith terminal brain cancer, which she eventually succumbed to in 1988, when Peter was eight. He sent Ravager Yondu Udonta to retrieve him moments after she passed away, but having found out that Ego killed all the other children that failed to contain his DNA, he instead chose to adopt him into his clan.