Arizona census numbers fail to meet expectations: How much will it cost the state? As it did 10 years ago, the U.S. Census Bureau overestimated Arizonaâs population. and last updated 2021-04-27 22:59:54-04 PHOENIX â The failure to gain a tenth congressional seat may be the least of Arizonaâs concerns involving the 2020 census data. As it did 10 years ago, the U.S. Census Bureau overestimated Arizonaâs population. This time by 3.5 percent. That is one of the largest discrepancies in the nation. Most experts believe these people exist, but because they werenât counted, there may be a real price to pay.