Complex sentence: In the 2010 United States Census, the city of Anaheim had a population of 336,265, making it the most populated city in Orange County, the 10th most-populated city in California, and ranked 54th in the United States.
Split into simpler sentences: In the 2010 United States Census, the city of Anaheim had a population of 336,265. It is the most populous city in Orange County, the 10th largest city in California, and the 54th-largest in the United States.