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Consequences of undocumented residents in the census—study shows trivial political impact

In recent years, some public figures have argued that undocumented residents in the United States should not be included in census data used for congressional apportionment because their inclusion unfairly benefits Democratic-leaning states.

John Robert Warren and Robert E. Warren analyzed data from every census from 1980 through 2020 and used high quality state-level estimates of the size of the undocumented resident population at each time point. The authors then calculated how many House seats and how many Electoral College votes would have changed had undocumented residents been excluded from the data after each census. The study is in the journal PNAS Nexus.

Previous efforts to address this question used projected rather than actual estimates and only considered the 2020 census. Using actual data from 1980–2020, the authors find that no more than five House seats or Electoral College votes would have switched states in any year if undocumented residents were removed and there were no years in which party control of the House or the outcome of a presidential election would have meaningfully changed.

In general, removing undocumented residents from census data used for apportionment would have had a trivial impact on party representation in the House or the outcome of presidential elections and is unlikely to have an increased impact in the future.