Who counts as white in the United States? This has been a demographic puzzle since US citizenship was first limited to “free white persons” in 1790. Over time, immigrants from various world regions began to comprise the white population, creating a numerical majority and what is now the widely used reference category for measuring racial inequality. This review traces the evolving composition of the white racial category from the 1960s to the present, highlighting increased immigration from Eastern Europe and the Middle East as key sources of diversity within the federally defined white population. I organize the review into three sections. The first section reviews the historical construction of the white racial category in relation to the federal classification system used by the US Census. The second section examines compositional changes in the global origins of white immigrants since the 1965 Immigration and Nationality Act. It highlights how geopolitical events have shaped divergent migration and resettlement experiences for immigrants from Eastern Europe and the Middle East—groups who are legally classified as white but often racialized as “not quite white.” The third section reviews research on immigration and health to illustrate how compositional changes in the white population affect our understanding of US health disparities. The conclusion considers the implications of treating whites as a single, monolithic group and calls for greater analytic attention to within-group diversity among whites in studies of inequality.