Next year’s census will determine the apportionment of House members and Electoral College votes for each state. To accomplish these vital constitutional purposes, the enumeration should count only citizens and persons who are legal, permanent residents. But it won’t.

Instead, the U.S. Census Bureau is set to count all persons physically present in the country—including large numbers who are here illegally. The result will unconstitutionally increase the number of representatives in some states and deprive some other states...