Charleston County went from 61.9% White and 34.5% Black in the 2000 Census to 64.2% White and 29.8% Black in the 2010 Census. The Black population of Charleston County actually went down from 107K to 104K.
True across the state, which went from 30% black to 27% black over the same period. Demographic changes will likely make SC more Republican over time.
So, is it that whites are moving in, blacks are moving out, or a combination of both?
It's a case of non-native whites moving in while both native whites and blacks are moving out to the suburbs, but not the same suburbs. The high-priced developments right along the coast are not surprisingly attracting more affluent people to them. Whereas the more reasonably priced inland suburbs of Dorchester and Berkeley Counties are getting the middle classes. The stratification that is going on in the developments is on socioeconomic lines, not racial, but obviously it does show up in the racial profiles.
It's just the popularity of beachfront property that is driving this, tho it plays a part. While it may have changed since then, I know that decade ago the Charleston County public schools had such an awful reputation that teachers preferred to work elsewhere. So basically if you're rich enough to move to where better schools are but not rich enough to send your kids to a private academy, you'll head across the county line to live.