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

CLAYTON, a county in the E. N. E. part of Iowa, bordering on Wisconsin, has an area of 760 square miles. The Mississippi river forms its entire boundary on the E. The Turkey river flows through the middle of the county into the first-named river, and the South fork of the Turkey traverses part of the county. The surface is diversified by rolling prairies and woodlands; the soil is productive, and the climate healthy. Timber and water-power are said to be abundant. In 1850, Clayton county produced 42,604 bushels of Indian corn; 36,860 of wheat; 25,701 of oats, and 3202 tons of hay. Mines of lead are worked in the S. E. part, near the river. The county is settling rapidly with Germans and others. Capital, Garnavillo. Population, 3873.