Fairfax, a N. E. county of Virginia, separated from Maryland and the District of Columbia by the Potomac river; area, 430 sq. m.; pop. in 1870, 12,952, of whom 4,284 were colored. The Occoquan river touches it on the S. W. The Orange, Alexandria, and Manassas, and the Washington and Ohio railroads pass through it. On the bank of the Potomac, in this county, and 15 m. below Washington city, stands Mount Vernon, the residence of George Washington. The surface is generally hilly. The soil in some places is sandy, and in others is nearly worn out; but there are many fertile and well cultivated districts. The chief productions in 1870 were 59,982 bushels of wheat, 295,330 of Indian corn, 120,072 of oats, 71,227 of potatoes, 8,097 tons of hay, and 178,345 lbs. of butter. There were 2,811 horses, 3,907 milch cows, 3,325 other cattle, 2,414 sheep, and 7,152 swine; 4 flour and 6 saw mills, 12 manufactories of carriages and wagons, and 2 of bricks. Capital, Fairfax Court House.