Complex sentence: The bulk of the city is in Dallas County, of which it is the county seat; however, sections of the city are located in Collin, Denton, Kaufman, and Rockwall counties.
Split into simpler sentences: The bulk of the city is in Dallas County, of which it is the county seat. However, sections of the city are located in Collin, Denton, Kaufman, and Rockwall counties.