Complex sentence: It was formed from parts of McLean, LaSalle, and Iroquois counties, and named after Edward Livingston, a prominent politician who was mayor of New York City and represented New York in the United States House of Representatives and Louisiana in both houses of Congress.
Split into simpler sentences: It was formed from parts of McLean, LaSalle, and Iroquois counties, and named after Edward Livingston, a prominent politician. He was the mayor of New York City, represented New York in the United States House of Representatives, then represented Louisiana in both houses of Congress.