PLAINFIELD, a city of the United States, in Union county, New Jersey, lies at the foot of Mount Orange, and on the left side of the Green Brook, a tributary of the Raritan. It may to some extent be regarded as a residential suburb of New York, from which it is distant 24 miles by the Central Railroad. The local manufactures—hats and clothing—are comparatively trifling. Laid out in 1735 and made a city in 1869, Plainfield had 5095 inhabitants in 1870 and 8125 in 1880. A railroad consisting of narrow iron bands nailed down to wooden logs was constructed between Plainfield and Elizabeth as early as 1838. Two miles to the south-west is Washington’s Rock, a coign of vantage from which the general used to watch the British movements.