The county was originally part of the county of Keokuk from 1837 to 1840 and was subsequently attached at different times to both Iowa and Mahaska counties. The first settler in Poweshiek County, after the Indians departed, was Richard B. Ogden who came in the fall of 1843. The county was formally organized on April 3, 1848, the date on which the first election was conducted. David Edmundson, John White, and John Rose, residents of the counties of Jasper, Mahaska, and Polk, were appointed commissioners for the purpose of locating a site for the county seat and providing for its establishment.
The county is named in honor of Chief Poweshiek, Fox-Mesquaki Indian Chief, who was for peace in the Black Hawk War. The present area of the county was said to be the hunting and fishing grounds for Chief Poweshiek.
Montezuma, the county seat, was laid out in June 1848. Early history says that in the settling of the county, it was thought that the northern part of the county would never be occupied. Therefore there was no difficulty in locating the county seat in the central township of the southern tier of the county.
The first courthouse was built in Montezuma in 1850. The courthouse was a two-story wooden structure with the courtroom on the first floor and the offices of the judge, clerk, sheriff and the treasurer on the second floor. A woodcut of the building shows that an outside stairway connected the two floors. This building was used as a courthouse, school, church, and a social gathering place until 1857. In 1857 the construction of the county’s second and current courthouse was begun, thus making it one of the oldest courthouses in Iowa. A property tax of one mill on the dollar was levied to pay for the building.
The newly constructed building was only the second permanent courthouse structure to be built in the state and is considered by the State Historical Society to be one of the finest examples of early courthouse architecture.
The total cost of this courthouse was $21,928.15. It is constructed of brick and its foundation, caps and sills are of limestone. Over the years the building has undergone several changes. In 1890 an addition was completed, and in 1933-1934 the courthouse was raised, and a full basement and new foundation were completed. This project cost approximately $15,000 to complete.