Modern mainstream United States populations have been little investigated by surname analyses. A sample of names in a suburban Detroit telephone directory yields a low proportion of random isonymy, as one would expect from the heterogeneous ethnic origins of such populations. However, they are not true breeding populations and actual matings may be considerably more inbred. The diverse origins of Americans and consequent large numbers of different surnames – said to be over a million – imply low levels of isonymy. Because of considerable polyphyly of surnames and the high rate of name-changing that has characterized immigrants to the United States, the random component of inbreeding is probably even less than implied by random isonymy. However, in the early stages of immigration of each new group, the group seeks to keep its identity and members tend to marry among themselves, so the inbreeding rates may be similar to those of the country of origin. In fact, if the immigrant group is small, inbreeding may be more intense than in the place of origin. This would be reflected in the non-random component of inbreeding in the first few generations. Except for a few groups with very strong religious sanctions against intermarriage, such immigrant enclaves in the United States dissolve after one, two or three generations in the melting pot of urban America.

The classic study of Arner (1908) in the United States has already been cited.