You may have noticed that the United States only actually counts the population every ten years. How do we track the population in the "intercensal" (noncensus) years? The Census Bureau and, in Utah, the Utah Population Estimates Committee must estimate population counts based on other data (home starts, school enrollment) etc. Obviously, estimation is an imperfect process and once true census counts are available, the estimated years need to be readjusted. (My own county of residence--Washington County--was subject to some noticeable revisions.)
The U.S. Census Bureau has just completed that process for states and counties and you can access those new "intercensal" estimates by clicking here. We'll be updating our products as soon as possible to reflect the new population figures.