Hamilton County, one of the western border tier, was erected by the act of March 6, 1873, which defined the boundaries as follows: "Commencing at the intersection of the east line of range 39 west with the 4th standard parallel thence south along said range line to its intersection with the north line of township 27 south; thence along said township line to the west boundary of the State of Kansas; thence north along said west boundary line of the State of Kansas to where it is intersected by the 4th standard parallel; thence east to the place of beginning."

In 1883, when several of the western counties were discontinued by act of the legislature, the boundaries of Hamilton were extended to include the western half of the present counties of Grant and Kearny and all of the present county of Stanton, but by the act of March 5, 1887, the original boundaries were restored. At present the county is bounded on the north by Greeley county; on the east by Kearny; on the south by Stanton, and on the west by the State of Colorado. It was named for Alexander Hamilton, one of the founders of the American republic, who was killed in a duel with Aaron Burr.

Pike's expedition of 1806 crossed the western boundary of Kansas in what is now Hamilton county; Long's expedition of 1820 passed through the county, and Fowler's journal of Glenn's expedition for Nov. 4, 1821, says: "We steered No 75 west 4 miles to [a point] of Sand Hills washed by the River and at Six miles farther to an island clothed With Willow and Cotton Wood—the main Chanel on the North Side of the Island the last 6 miles of our Corse Was West," etc. Coues thinks the 16 miles of this day's march took the expedition past the site of the present city of Syracuse, and that the camp of the 4th was not far from the present town of Coolidge. Fort Aubrey (q. v.) was established not far from Mayline in the late summer of 1865 and was occupied as a military post until the following spring.

The first permanent settlement in the county was made by a colony from Syracuse, N. Y. The colony was organized there on Oct. 23, 1872, and a committee, consisting of Evelin P. Barber, S. R. Jones and D. G. Ackland, was sent forward to Kansas to select a location. On Christmas day the committee decided on a tract of land in Hamilton county, though that was before the county had been created by legislative enactment. The main body of the colony arrived on the site on March 23, 1873. These colonists tried to have the name of the county changed to Onondaga, after their old county in New York, but the legislature declined to comply with their request. Following the New Yorkers came some Mennonites and other settlers, and by the beginning of 1886 an agitation was commenced for the organization of the county.

Early in that year a memorial signed by 250 citizens of the county was presented to Gov. John A. Martin, who appointed Alfred Pratt to take a census of the county. The census showed a population of 1,893 people, of whom 614 were actual householders, and on Jan. 29, 1886, the governor issued his proclamation declaring the county organized. At that time the county embraced Stanton and the portions of Kearny and Grant above mentioned. The governor appointed as commissioners J. H. Leeman of Hartland, Lawrence W. Hardy of Medway, and Dennis Foley of Syracuse. Thomas Ford was appointed county clerk, and Kendall was designated as the temporary county seat.

A bitter contest soon arose between Kendall and Syracuse for the permanent seat of justice, and an element in the fight was the question of restoring the old county lines by the reëstablishment of the counties of Grant, Kearny and Stanton. At an election on April 1, 1886, Syracuse was declared the county seat, but Kendall charged gross frauds on the part of the advocates of Syracuse and appealed to the supreme court. That tribunal threw out the vote of Syracuse township and ordered the county officers to take their offices back to Kendall until another vote could be taken at the general election the following November. At the November election the vote for county seat stood: Syracuse, 785; Kendall, 390; Coolidge, 224; Johnson City, 93; Scattering, 4, giving Syracuse a majority of 74 over all competitors. At the same election the following county officers were chosen: Representative, J. T. Kirtland; probate judge, W. C. Higgins; clerk of the district court, W. P. Humphrey; county clerk, J. M. Hicks; sheriff, C. C. Mills; treasurer, J. H. Bentley; register of deeds, J. P. Gardner; county attorney, G. N. Smith; county superintendent of schools, C. N. Gartin; surveyor, J. W. Beatty; coroner, J. N. Slown; commissioners, L. C. Swink, A. A. G. Stayton and S. S. Taggert.

Hazelrigg's History of Kansas (p. 224) says the fight for the county seat was kept up for some years, two sets of county officers being elected and the county records divided, until the question was finally decided by the supreme court in favor of Syracuse.

The surface of the county is level in the northern part and rolling prairie in the southern. The Arkansas river enters the county from the west, near the center, and flows in a southeasterly direction until it enters Kearny county. Along this river the bottom lands are from 2 to 4 miles wide. There is little native timber, but a number of artificial groves have been planted. White magnesian limestone is abundant in the bluffs along the river and some gypsum deposits have been found. The Atchison, Topeka & Santa Fe railroad runs along the north bank of the Arkansas river, giving the county a little over 28 miles of railroad. The county is divided into eight townships. viz.: Bear Creek, Coolidge, Kendall, Lamont, Liberty, Medway. Richland and Syracuse. In 1910 there were 27 organized school districts in the county, with county high schools at Coolidge and Syracuse. The population of the county in that year was 3,360, a gain of 1,934 during the preceding decade—over 100 per cent. The value of taxable property was $5,257,355, and the value of farm products, including live stock, was nearly $372,500. The principal crops are broom-corn, milo maize, hay (including alfalfa), sorghum and wheat.