The popularity of a name largely depends on the political situation in the country, and from the pop culture of the period. You want to know how each of the states preferred to call the children in a given year, since the distant 1910? Mike Barry has created an interactive map, which can be traced back a long way for each of the currently popular male and female names. We will not burden this stuff with a bunch of pictures of every single year, but only to make a selection with a difference of 20 years for each sex.
As you can see, name Mary was most popular in 1910.
Mary still was popular in 1920, but Betty has a strong 2nd position.