From Halopedia, the Halo wiki
Presumably Outer Colonies
Charles VanKeerk was an Insurrectionist during the Human-Covenant War. Sometime after Sam's death, VanKeerk wrote a letter to Sam's wife Amy offering his condolences. In the letter, he expressed anger at the UNSC's control and their inability to protect the Outer Colonies.
Based on his surname, he may be of Dutch descent.