Complex sentence: It has 14,027 full-time employees, 5,925 of whom are teachers, the district is the county's and state's largest employer and one of the largest in the US (at least in school systems).
Split into simpler sentences: It has 14,027 full-time employees, 5,925 of whom are teachers. The district is the county's and state's largest employer and one of the largest in the US (at least in school systems).