February 5, 1844 marks the beginning of Mahaska County's history. On that date Iowa's Territorial Legislature enacted the law authorizing the organization of a county named Mahaska, after one of the most noted chiefs of the Indian nation known as the Ioways. By this law Mahaska County became two years older than the State of Iowa. William Edmundson, receiving his appointment from the Territorial Assembly, became the first sheriff and justice of peace and was charged with the organization of the twenty-four mile square county. With the help of his clerk, Micajah T. Williams, these two officers divided the county into nine precincts, and by the first Monday in April 1844, an election was held for county officers.
On May 11, 1844 a Commission of three men, appointed from Iowa's Assembly, selected a site for the county seat. The location was the narrowest point on the divide between the Des Moines and Skunk rivers, known as the "Narrows." They left the naming of the new town to the local Board of County Commissioners, who chose the name of Oskaloosa, meaning "last of Beautiful" in honor of a Creek Indian princess.
The County Commissioners, by May 14, 1844, had chosen the grand and petit jurors for the first term of the District Court to be held July 1, 1844. The courtroom was an unfinished log cabin built by William D. Canfield and located within the present limits of Oskaloosa. The first Court House owned by the county was a two-story frame structure built at the northwest corner of the square and occupied in January 1846. It was abandoned in 1855 and thirty years passed before the first permanent Court House, now located east of the square, was built at a cost of $132,500 and dedicated on February 27, 1886.
The county's first school was opened in a crude, doorless cabin in the timber two and one-half miles east of Oskaloosa on September 16, 1844, with Miss Semira Ann Hobbs as teacher. As early as 1844, Quaker and Methodist as well as other religious groups, were established in the county, and in 1846 the Cumberland Presbyterian Church was built in Oskaloosa.
On July 2, 1850, the first issue of the Iowa Herald (now the Oskaloosa Herald) was published by Needham and McNelley. The New Sharon Star was founded in 1873.
Coal mining brought the county its first source of wealth. Twenty-two communities have been surveyed for town sites, but only Oskaloosa, New Sharon, Eddyville, Fremont, University Park, Keomah Village, Leighton, Barnes City, Beacon and Rose Hill, now enjoy the status of being incorporated towns. Most of the rest have become ghost towns and are now memories with the exception of the town of Cedar with a Post Office established in 1873. Other unincorporated towns are Evans, Wright, Peoria, Lacey and Taintor.
Three schools of higher learning have been located in the county. The Iowa State Friends Association founded Iowa Union College in Oskaloosa in 1863, and ten years later re-named it Penn College. Oskaloosa College, supported by the Christian Church, was built in 1864. After twenty years service, the equipment was moved to Des Moines to help establish Drake University. In 1906 on a 220-acre tract of land east of Oskaloosa, the Central Holiness University was opened. After several changes in administration, it was named Vennard College (1959) and is located in University Park.
The first County Fair was held in the public square on October 23, 1852, and in 1861 the traveling State Fair was held in Oskaloosa.
During the County's first years vehicles were scarce. Sheriff Edmundson owned the only buggy; traveling was done horseback or by horse-drawn wagons. Oxen were used extensively in breaking prairie and local hauling. By 1860 the Western Stage Company was doing a thriving passenger business into the county seat from the "River" since traveling time was one to two days according to conditions of the road. The Des Moines Valley railroad reached the county in 1864, connecting the community with Eddyville. The Iowa Central railroad came in 1871.