The site for the future seat of Iowa County was selected in 1845. The town site was then surveyed and lots were put on sale in October of the following year. The location of the town plat was in a section of open prairie just south of the Iowa River, east of its confluence with Big Bear Creek. Andreas noted in 1875, “The Town is built around a public square, three hundred feet on each side, which is enclosed with a good fence, and set with a variety of shade trees, including numerous evergreens.”
39Some twelve years after its founding, in 1857, the Rock Island and Pacific Railroad arrived at Marengo. The town's first great period of growth was in the years immediately after the end of the Civil War when 150 dwellings were built between 1865 and 1866. In the 1920s Marengo became a stopping point on the east west US 6. With the construction of Interstate 80, 8 miles south, the town is now off the normal travel route.