The first settler to be born (July 1836) in what became Jefferson County was William Coop, son of Col. W. G. Coop. Enough settlers had moved into this territory by 1838 that the Territory of Iowa was approved by Congress on June 12, 1838, having been created from the Wisconsin Territory, which, in turn, had been created from land acquired in 1803 as part of the Louisiana Purchase.
Jefferson County came into being on January 21, 1839, as the result of an act ("An act to divide the county of Henry and establish the county of Jefferson") presented by Col. W. G. Coop to the Iowa Territorial Legislature.
Three Commissioners were appointed, whose first task was to locate and establish the seat of Justice of Jefferson County. Fairfield was chosen (over Lockridge as Col. Coop wanted), largely because of its central location and pleasant setting on an elevated prairie. Although Henry B. Notson had some sort of claim on the land, he relinquished it, and the town was laid out in April 1839. Fairfield was incorporated in 1847.
The first election of County Officials was held on the first Monday of April 1839, when three County Commissioners, a Treasurer, a Sheriff, a Recorder and a Surveyor were elected.
A change was made in 1851 - a County Court was created by the State of Iowa (Iowa became a State of the Union on December 28, 1846), which gave the County Judge powers previously exercised by the Board of County Commissioners.
But on March 22, 1860, the State Legislature passed an act creating a Board of County Supervisors for each county, replacing the powers of the County Judge. An elected Supervisor from each township served on the Board, but this system was not popular and in 1871 the law was changed to a three-member Board of Supervisors.
A wooden courthouse was completed in December of 1839, but it was moved to allow a stone and brick courthouse to be built (completed in January, 1851). The current courthouse was built in 1892 at a new location. Details are on the Fairfield heritage Tour.
A house considered to the oldest remaining white settler's cabin in Iowa was built near Lockridge. See details on the Louden Tour.
(Excepted from History of Jefferson County, Western Historical Company, 1879)
The IAWebGen Project website has:
A photo of the 1st county courthouse (scroll down),
First families of Jefferson County,
A look at farm life in northeastern Jefferson County in 1888,
And much more.