O’Brien is on of the far northwestern counties created by wholesale in 1851. At that time, there was no settler within its prescribed bounds. There was, however, quite a large contingent of Irishmen in the Legislature, and the projected county was named after William O’Brien, one of the leaders of 1848 who was urging the establishment of Ireland as a republic. The first white settlers in the county were Hannibal H. Waterman and family. Both Mr. and Mrs. Waterman were born in Cattaraugus County, New York, but never met until the fall of 1852 when they became acquainted in Bremer County, Northeastern Iowa. There they were married in June, 1854, and two years later settled a short distance south of the mouth of Waterman Creek on the banks of the Little Sioux River. Mr. Waterman was a lumberman, a farmer and a Methodist exhorter, and a tall, powerful, magnetic blonde, wearing a full beard - altogether a striking man of strong character.
When Mr. and Mrs. Waterman arrived in Southeaster O’Brien County, in July, 1856, they had one child, an infant daughter. On the 30th of May, 1857, they had an addition to their family, in the person of Anna Waterman, who was the first native white child of O’Brien County. But Mr. Waterman was not long to be left in peace as a simple God-fearing settler; for in 1859 appeared at his cabin two professional politicians, James W. Bosler and J. W. Dorsey, both later to be connected with the Star Route frauds and extensive cattle interests in New Mexico. They temporarily hailed from Sioux City, and later seven or eight others from that place arrived to hold an organizing election at Mr. Waterman’s house, the only building in the projected county. A log cabin was built directly in front of Waterman’s house, and four of the officers elected in February, 1860, boarded with him. Waterman himself, in order that all the offices should go ‘round, had been chosen treasurer, recorder and superintendent of schools. In the summer of 1860, about a dozen men from Fort Dodge came up to the county seat of O’Brien and protested the supremacy of “the Sioux City gang.” Mr. Waterman sided with the Fort Dodge people, believing that they intended to become settlers and not political adventurers, and had his claim jumped by the Sioux City men. The result was that the county was exploited most shamefully for a number of years; it was considered a bone with some meat attached, worthy of being fought over by hungry dogs.
Most of the settlers, fairly permanent or otherwise, had located in the southeast corner of the county, where the village of O’Brien had been platted as the “seat of justice.” As the population spread into other sections of the county, it became necessary to locate the seat at a more convenient point than O’Brien. At an election held in November, 1872, it was resolved to locate the seat of justice at the center of the county, where a town was laid out for that purpose. When it came to naming it, the plan was adopted of taking the first letters in the names of the county officials and several other prominent citizens, with the following result: O'BRIEN COUNTY lies in the second tier east of the western boundary of the State and also in the second south of the Minnesota line. It is twenty-four miles square, containing an area of five hundred seventy-six square miles and was originally one vast prairie, entirely destitute of timber with the exception of a few small groves along the Little Sioux River in the southeast corner. The county was created in 1851 from territory belonging at one time Fayette and was named for William O'Brien, one of the leaders for the independence in Ireland in 1848.
The first white settlers in the county were H. H. Waterman and family who came from Bremer County and settled in a grove in the southeast corner of the county on the banks of the Little Sioux River in 1856. Other settlers entered claims in the vicinity and in 1860 a county government was organized by the election of the following officers: J. C. Furber, judge; H. H. Waterman, treasurer and recorder; Archibald Murray, clerk and surveyor.
The first county-seat was O'Brien, a village in the southeast corner of the county, in the vicinity of most of the settlers. Here the first term of the District Court was held by Judge Henry Ford. The first school was taught by Mrs. H. H. Waterman and for some time religious meetings were held in the Waterman cabin. The O'Brien Pioneer was the first newspaper which was published by B. F. McCormack and J. R. Pumphrey. At an election held in 1872, it was decided to locate the permanent county-seat in the center of the county where a town was laid out by the county officers. The name for the town was fixed upon in the following manner: the first letter of the names of the officials and a few others was taken-Pumphrey, Roberts, Inman, McCormack, Green, Hays, Albright and Renok. These, P-R-I-M-G-H-A-R, made the name of the new county-seat. The first house was built by J. R. Pumphrey for the use of the county. A hotel was erected by C. F. Albright. In 1873 the Sioux City and St. Paul Railroad was built through the county and the town of Sheldon was laid out upon the line in the northwest part of the county.