McCarthy's population averaged 35 between 2000 and 2010. The population in 2000 was 42, while the population in 2010 was 28. This change represents a 33 percent reduction in population over the 10-year period.
McCarthy has become more ethnically diverse over the same period of time. In the 2000 census, 100 percent of the residents described themselves as being white. However, in the 2010 census, 27 of the residents described themselves as being of white ethnicity, and one person reported being of two or more races. None of the residents considered themselves as being of Hispanic or Latino origin, however.