The 1854 Gazetteer of the United States by Thomas Baldwin shows:

UNION, a county in the S. part of Arkansas, bordering on Louisiana: area about 1230 square miles. It is bounded on the N. W. by Washita river, and drained by Sulphur creek, and the North fork of the Bayou D'Arbonne. The surface is moderately hilly; the soil is sandy and productive. Cotton and Indian corn are the staples. In 1850 it produced 7037 bales of cotton; 341,406 bushels of corn; 93,660 of sweet potatoes, and 33,861 pounds of butter. The quantity of sweet potatoes was the greatest produced in any one county of the state; and the quantity of cotton greater than in any except Chicot county. It contained 14 churches, and 1 newspaper office. The Washita river is navigable by steamboats. In 1850, Union was the most populous county in the state. Capital, El Dorado. Population, 10,298; of whom 5531 were free, and 4767, slaves.