Complex sentence: Iles, who moved to Springfield in 1821, was one of the city's earliest settlers; he ran the first store in Sangamon County and helped persuade the county to locate the county seat in Springfield.
Split into simpler sentences: Iles, who moved to Springfield in 1821, was one of the city's earliest settlers. He ran the first store in Sangamon County and helped persuade the county to locate the county seat in Springfield.