SIOUX, (usually pronounced soo.) a new county in the W. N. W. part of Iowa, has an area of about 1100 square miles. It is bounded on the W. by the Sioux river, and also drained by the head waters of Floyd's river, an affluent of the first-mentioned stream. This county is not included in the census of 1850. County seat not located. (Baldwin's New and Complete Gazetteer of the United States..., 1854)
SIOUX COUNTY Was organized in 1860. It is on the western boundary of the State, the second county from the northern boundary line. It is bounded on the north by Lyon County, on the east by O'Brien, on the south by Plymouth, and on the west by Nebraska. It has but few settlers, and there is as yet a large quantity of vacant Congress land, of good quality. The bottom lands on the Big Sioux lie generally beyond the reach of overflow, and are of the best character. There is considerable rough lands, and some gravelly and sandy knolls dispersed through the county, gravelly near Rock River, in the northwestern part, and sandy loam in the south part of the county.
CALLIOPE is the county seat. (Hair's Iowa State Gazetteer..., 1865)