Objectives This article uses craniometric allocation as a platform for discussing the legacy of Samuel G. Morton's collection of crania, the process of racialization, and the value of contextualized biohistoric research perspectives in biological anthropology. Materials and Methods Standard craniometric measurements were recorded for seven Seminoles in the Samuel G. Morton Crania Collection and 10 European soldiers from the Fort St. Marks Military Cemetery; all individuals were men and died in Florida during the 19th century. Fordisc 3.1 was used to assess craniometric affinity with respect to three samples: the Forensic Data Bank, Howells data set, and an archival sample that best fits the target populations collected from 19th century Florida. Discriminant function analyses were used to evaluate how allocations change across the three comparative databases, which roughly reflect a temporal sequence. Results Most Seminoles allocated as Native American, while most soldiers allocated as Euro‐American. Allocation of Seminole crania, however, was unstable across analysis runs with more individuals identifying as African Americans when compared to the Howells and Forensic Data Bank. To the contrary, most of the soldiers produced consistent allocations across analyses. Repeatability for the St. Marks sample was lower when using the archival sample database, contrary to expectations. For the Seminole crania, Cohen's κ indicates significantly lower repeatability. A possible Black Seminole individual was identified in the Morton Collection. Discussion Recent articles discussing the merits and weaknesses of comparative craniometry focus on methodological issues. In our biohistoric approach, we use the patterning of craniometric allocations across databases as a platform for discussing social race and its development during the 19th century, a process known as racialization. Here we propose that differences in repeatability for the Seminoles and Euro‐American soldiers reflect this process and transformation of racialized identities during 19th century U.S. nation‐building. In particular, notions of whiteness were and remain tightly controlled, while other racial categorizations were affected by legal, social, and political contexts that resulted in hybridity in lieu of boundedness.