Source: "Parnell Centennial: 1885-1985 - 100 Years in Little Ireland"

Marengo was made County Seat August 4, 1845. The name Marengo was suggested by the Territorial Commissioners becasue it was supposed to resemble the Valley of Iowa River to that of "Marengo in Italy" where Napoleon Bonaparte gained celebrated victory. The name was unsatisfactory to many of the settlers and the Commissioners ordered that it should be Valley Forge instead of Marengo, but there was considerable opposition to the change so it remained Marengo.

Marengo was selected for a town site because the place granted transportation and good mill sites for industry on the Iowa River. By 1860 there were several mills operation on the northeast corner of town, along with all kinds of allied industries for transportation on the Iowa River.

Close at hand was timber for lumber, trapping and fur trade, productive soil, and an overflow of investors from Iowa City, who saw the advantages of the river on the City of Marengo.

The first courthouse, a one-room log structure located on the north side of the public square, was built April 14, 1847, for $50. The second courthouse was built in 1849 for $600 on the east side of the public square. It was more elaborate. The third courthouse was built in 1861 for $2,000 and made of brick. The present county courthouse is the fourth. It was built 1892-1893.

Opponents of Marengo had attempted in early years to move the county seat to Genoa Bluffs; and in later years to Williamsburg. Arguments for change gained  credence becasue the river and Big Bear Creek flooded Marengo and people sometimes had to go to court in boats in and out of the upstairs windows of the court house. The proposition was beaten by a slender majority of five votes and those who favored the move time gracefully submitted to the will of the people.