In the second half of the 20th century, the USA faced the problem of polarizing society. It is expressed, among other things, in political preferences. With the development of transport infrastructure and income increase, Americans began to migrate more often, choosing for residence areas with people with similar politic views. Such migrations form electorally homogeneous regions, which may eventually lead to isolationism and even tribalism. This phenomenon is called “The Big Sort”. The study proposes to identify the dynamics of polarization of the American nation, as well as agglomerations with different electoral preferences using a new quantitative method – Partisan Voting Index.