Republicans have since not come close in Loudoun in a statewide race. In the 2017 contest for governor, Northam beat Gillespie in Loudoun by more than 23,000 votes.

Arlington County: The smallest of Northern Virginia’s big four counties, Arlington is projected to gain about 46,000 residents in the 20-year span, rising from 249,298 in 2020 to 295,383 in 2040.

Arlington has not voted for a Republican in a statewide election since 2002, when it backed Sen. John Warner, R-Va., against two independents. Warner received 83% of the statewide vote in that contest.

Richmond area

Chesterfield County: Chesterfield, which leads population growth in the Richmond area, is projected to gain nearly 80,000 residents — from 353,841 in 2020 to 433,508 by 2040. At that point it would be gaining on Virginia Beach, long the state’s most populous locality outside Northern Virginia.

Chesterfield was a Republican stronghold in statewide elections for years, but its voting patterns have begun to change. Republican Donald Trump carried the county by about 4,000 votes in the 2016 presidential election. GOP nominee Mitt Romney had carried Chesterfield by more than 13,000 votes in 2012.