(I do not have all the data to calculate the gray counties/independent cities’ Partisan Voting Indexes (PVIs)).
In the early 20th century Virginia was mostly Democratic except the southwest, which was more Unionist and Republican. In the 1930s Virginia actually became less Democratic earlier than most of the other southern states because of Republican trends in the Appalachian counties along West Virginia.
Much of the state swung Republican in the 1960s and early 1970s. Virginia became a little less Republican in 1976 when Jimmy Carter (D) first ran, but still voted for Gerald Ford (R). Democratic strength began to solidify in the black-majority counties in the southeast, Richmond, union-influenced Roanoke, and college towns like Charlottesville and Blacksburg (in Montgomery County, the only light red county in the southwest in the later maps). Danville, on the southern border, became Democratic in the 2000s as whites moved out and it became majority-black.
In the 1990s, Alexandria and Arlington in Northern Virginia became blue. The rest of the area began trending that way in the 2000s as many college-educated voters moved to the rapidly-growing Washington DC area. Fairfax’s PVI turned blue in 2004, followed by Prince William in 2008 and then Loudoun in 2012. The area became bluer in 2016 as most of the southwestern/Appalachian counties turned dark red, including historically Democratic counties such as Buchanan and Dickinson.
Here are the results in table format.
Here are the results in slide format.