Simplify the following text for a Grade 5 native English-speaking person.
Original: North Charleston is the second largest city in the metropolitan statistical area of Charleston and ranks as the third largest city in the state ; Mount Pleasant and Summerville are the next largest cities . These cities combined with other incorporated and unincorporated areas surrounding the city of Charleston form the Charleston-North Charleston Urban Area with a population of 423,410 as of 2000 .
Simplified: Charleston is a city in Berkeley and Charleston counties in the U.S. state of South Carolina .