In addition to the above map and article for mental_floss, below is a list of the top 5 most distinctive last names by state. This is a larger subset of the same data. To keep the map readable, only the most distinctive last name for each state was used for the infographic. However, some readers may wish to dig deeper.
Methodology: The starting point is the top 250 most prevalent last names based on the nationwide total. From these 250 names, the “distinctive ratio” is calculated as follows for each last name in every state + DC: (last name prevalence in state) / (last name prevalence in US). The higher the distinctive ratio, the more “distinctive” a last name is considered for the purposes of this analysis.
The last name with the highest distinctive ratio in each state is what is on the map. The top 5 highest are shown in the list.
My data source is the Social Security Death Master File, courtesy of SSDMF.INFO. The list is widely used as a death verification tool, but a fraction of a percent of the individuals are added erroneously while still alive. 80% of these are people who were born 1930 or earlier. The geographic distribution is derived from the three digit social security number prefix for individuals with a year of birth 2010 or earlier. That is prior to the year when the SSA implemented randomization. Strictly speaking, this represents the state in the mailing address on the social security number application form, which is not always the state of birth or state of residence.