This question is for Germans. Please answer!?

Ok, so I saw someone on Facebook and they had a regular American last name. I'm not going to give out their name but lets pretend thein name was Jacob Harold. Then he put "von" in between his name so then it look like Jacob von Harold. I know it's common for some Germans to have "von" in the middle of their name but does it still make it German if you put it in any last name. I'm kind of confused on this. Hope it makes enough sense to be answered. Thanks.