Virginia is a relatively new entrant to the swing states' club, having reliably gone Republican for decades before President Obama moved it into the Democratic column in 2008. Nevertheless, changing demographics have led both sides to lavish millions in ad spending and many hours of campaigning on the Old Dominion State, whose 13 electoral votes are very much in play.

Mitt Romney is likely to clean up in the more rural, less populous counties in the southern and western parts of the state. More indicative of the state’s overall lean will be larger counties that offer a combination of suburban and rural areas and have changed hands over the last two presidential elections.

Foremost among these are Loudon, Prince William and Henrico counties, according to Geoffrey Skelley, a political analyst at the University of Virginia’s Center for Politics. All three backed George W. Bush in 2004 but flipped to Obama in 2008.

Prince William and Loudon both lie in the suburban sprawl radiating outward from Washington, D.C., but are more toss-ups than other suburban hubs like the city of Alexandria or Fairfax County, which have reliably broken for Democrats. Henrico is on the outskirts of Richmond, another city that went for Democrats in huge margins in both 2004 and 2008.

Those three counties bear watching because of significant minority populations, Skelley said. The state’s Hispanic population nearly doubled between 2000 and 2010, and while it only accounts for about 8 percent of the electorate, Obama still has a hefty lead among Latino voters. Obama will need to capitalize on that advantage in Prince William County, win over black voters in heavily African-American regions like central and eastern Henrico county, and fare well in Loudon’s diverse suburbs, Skelley said.

“For Obama, it is critical that he put up similar numbers to his 2008 totals in the precincts in these areas,” Skelley wrote in an email.

The other key Virginia region to watch is the Hampton Roads metropolitan area, the heavily populated cluster around Norfolk and Virginia Beach. Its year-round harbor makes it home to a vast ring of military facilities and shipyards, which has led Romney to campaign heavily there as he seeks to tie Obama to impending military “sequestration” cuts.

Hampton Roads has also flipped allegiances over the past two elections, going for George W. Bush in 2004 by a margin of about 40,000 votes and then backing Obama over John McCain by some 90,000 votes. In both cycles, it accounted for about 20 percent of the overall vote in Virginia.

Virginia is also in the midst of a heated Senate race featuring two former governors, Democrat Tim Kaine and Republican George Allen. The presidential race could have a down-ballot ripple effect on that contest.