Don't feel too bad. I live in SC and 9 out of 10 friends consistently think that I live in NC (no matter how many times I correct them). For some reason when people hear Carolina, they automatically think of the northern one.
ETA: You would think with the popularity of LivePD and the fact that two departments featured are located in SC that they'd remember us. Especially when so much crazy stuff goes down with those two departments in particular. Also, now that I think about it... a portion of Cayce is in Richland County!