Maricopa County ( ) is a county in the south-central part of the U.S. state of Arizona. As of the 2010 census, its population was 3,817,117, making it the state's most populous county, and the fourth-most populous in the United States. It is more populous than 23 states. The county seat is Phoenix, the state capital and fifth-most populous city in the country.
The U.S. state of Arizona has a population, according to the 2010 census, of 3,817,117.
The reason that this is incorrect is because the population total referenced is actually the population of Maricopa County according to the 2010 census, not the entire state of Arizona.  I believe that this was difficult for the system to pick up because all the pertinent pieces of information exists in the original statement but was unable to detect the omission of the Maricopa County detail.