The news site Politico lists St. Louis County as one of the five most important counties in the country for either Democrat Barack Obama or Republican John McCain.

“McCain will likely win rural Missouri and Obama will win the big urban bookends, St. Louis and Kansas City,” the Politico’s Charles Mahtesian writes today. “But McCain also needs to keep Obama from outperforming John F. Kerry’s 55 percent in Democratic-leaning suburban St. Louis County, which is the most populous in the state — and which doesn’t include the city of St. Louis within its borders.”

Though many parts of St. Louis County are more Republican-leaning, the point is the same: The candidate who wins Missouri — listed as a toss-up coming into today — will benefit from cutting into their opponent’s base.

Another county listed as one to watch by Politico is Greene County, Mo. — which includes Springfield, where Obama and wife Michelle campaigned Saturday night.