Complex sentence: Caddo County is home to more than 451 archaeological sites, of which 115 are known to relate to the Plains Village era (A.D.1000 to 1500).
Split into simpler sentences: Caddo County is home to more than four-hundred-and-fifty-one archaeological sites. One-hundred-and-fifteen of those sites are known to relate to the Plains Village era (A.D.1000 to 1500).