Springfield, Illinois is 2.3 times larger than Round Rock, Texas.
Area: 88 km2 calculated
Round Rock is a city in the state of Texas within the Greater Austin, Texas metropolitan area and Williamson County. The 2013 census estimate places the population at 109,821. Wikipedia
Area: 205 km2 calculated
Springfield is the capital of the US state of Illinois and the county seat of Sangamon County with a population of 116,250, making it the sixth most populated city in the state. It is the largest city in central Illinois. Wikipedia