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

DE WITT, a county in the central part of Illinois, has an area of 675 square miles. It is drained by the head streams of Salt creek, an affluent of the Sangamon river. The surface is generally level, and diversified by prairies and forests of good timber: the soil is highly productive and easily cultivated. Indian corn, wheat, oats, potatoes, and pork are the staples. In 1850 there were raised 704,600 bushels of corn; 22,401 of wheat; 45,737 of oats; 2083 tons of hay, and 18,833 pounds of wool. It contained 6 churches, and 8941 pupils attending public schools, Stone coal is found. The county is intersected by the Illinois central railroad. The name was given in honor of De Witt Clinton, governor of New York. Capital, Clinton. Population, 5002.