Wyandotte County, located in the extreme eastern part of the state, was formed from the southeastern part of Leavenworth county by an act of the legislature of Jan. 29, 1859, with the following boundaries: "Commencing at a point in the middle of the channel of the Missouri river, where the north line of the Delaware reserve intersects the same, running thence west, on said reserve line, to the line between ranges 22 and 23; thence south on said range line, to the south boundary of Leavenworth county; thence easterly, on said boundary, to the middle of the main channel of the Missouri river; thence northwesterly, with said main channel, to the place of beginning; also that portion of Johnson county, lying north of the township line between townships 11 and 12, east of range 23."

Wyandotte is the smallest county in the state, having an area of only 153 square miles. It is triangular in shape, being bounded on the north by Leavenworth county and the Missouri river; on the east by the Missouri river; on the south by Johnson county, and on the west by Leavenworth county. It was named in memory of the Wyandotte Indians. At the present time the county is divided into the following townships: Delaware, Prairie, Quindaro, Shawnee and Wyandotte. The general surface of the country is undulating, marked by high bluffs along the Kansas and Missouri rivers, in the early territorial days, the eastern portion of the county was heavily timbered with cottonwood, hickory, oak, walnut and other varieties of trees native to Kansas. The main water course is the Missouri river, and the next stream of importance is the Kansas river, which forms a part of the southern boundary, and then flowing northeast empties into the Missouri river at Kansas City. It separates the two southeastern townships from the remainder of the county. Springs are found in all portions of the county and well water can be obtained at an average depth of 35 feet. Limestone, sandstone, fire clay and cement rock are found in considerable quantities. Coal has been reached at a depth of 300 feet and is mined for commercial purposes. The soil is a rich sandy loam, especially well adapted to fruit raising. Agriculturally the county ranks high; winter wheat, corn and oats are important crops and it is the "banner" county in the production of Irish potatoes. There are over 300,000 fruit trees of bearing age, apple and peach being the leading varieties.

The portion of Wyandotte county lying south of the Kansas river, with the exception of a tract reserved by the government, which it is supposed was intended for military purposes, once belonged to the Shawnee Indians. (See Indians and Indian Treaties.)

It is not known positively in what year the first white men visited this part of Kansas, but it was early in the 18th century, when the lower part of the Missouri river, as far as the mouth of the Kansas, was explored by the French. A few years later there were at least 100 couriers des bois living and trading with the Indians along the Missouri river. In 1703, Charles Le Sueur was sent to the headwaters of the Mississippi on a mining expedition and on his return in 1705, passed up the Missouri as far as the mouth of the Kansas. Lewis and Clark passed along the eastern boundary of the present county in 1804, on their exploring expedition for the government. They discovered a number of old Kansas villages, among them an ancient village site a little east of White Church.

So far as is known, the first white men who established themselves permanently in the county, were the Chouteau brothers, Indian traders, who built their first trading post in what is now Wyandotte county in 1812. Cyprian Chouteau subsequently built several other trading posts north of the Kansas river, the most important being the famous "four houses." The Methodist mission among the Delawares was founded in 1831, and the Baptist mission the following year. The first church in the county was erected as a mission in 1832, in a beautiful grove located on the high divide where the town of White Church now stands near the center of the present county, about 8 miles west of Kansas City. The missionaries in charge of the churches and schools were the second whites to locate permanently. The Wyandots were civilized when they came to Kansas from Ohio in 1843. The farms they opened, the homes they built, the schools and churches they established were as good as similar institutions among the whites of the frontier, and in many cases better. The city of Wyandotte (now forming a part of Kansas City, Kan.) was started by the Wyandots soon after they located on the reservation in 1843, by the erection of a company store and a cabin for the United States agency. In fact, within two years this settlement was a flourishing frontier town. On July 1, 1844, the first free school in what is now the State of Kansas was opened at Wyandotte by J. W. Armstrong. The first school building was a frame structure on what is now Fourth street, sometimes called the council house, because the Wyandot nation met there. In 1843 occurred a notable event in the marriage of Hiram N. Northrup and Margaret Clark, daughter of the Wyandot chief. Fruit trees were planted on the reservation as early as the spring of 1845, and the members of the tribe continued to make improvements along all lines.

The conflict between the pro-slavery and anti-slavery people began to rage in the Wyandot nation six years before it became the vital question in the territory. In 1843 their Methodist missionary preached against emancipation, and four years later became active in the organization of a "Church South" among them, a church which was supported by the most pronounced pro-slavery men. The majority of the nation refused to join this church when it was organized, and when the minister appointed from the northern conference was stoned from the church he held services out of doors until another church was built. The hostility between the two branches of the church continued to be that of the opposing political parties, until it reached its height in 1848, and as a result drunkenness and disorder increased among the members of the tribe. This led to the formation of a temperance society, the first in what is now the State of Kansas, and a log jail was built at Wyandotte, where drunken Indians were confined.

In 1849, when the gold rush to California began, Wyandotte and the trading posts of the Chouteaus became the outfitting posts for many of the parties starting west. Thousands passed through the county, but few settled there, being lured west by the call of gold. Many Mormons also passed through the county.

It was among the Wyandots that the first agitation occurred looking toward a territorial organization. (See Boundaries.)

The political history of Wyandotte county begins with the first election, held in June, 1857, for a delegate to the Lecompton constitutional convention. In October of the same year the region came into general notice because of the stuffing of the ballot box and other frauds during the election held at the Delaware crossing, 8 miles west of Wyandotte. By the act creating the county in 1859, Wyandotte was named as the temporary county seat. The county was organized on Feb. 25, when the county commissioners, George Russell, and George Veale (acting in place of Alfred Gray) first met. They appointed Myron J. Pratt secretary, canvassed the votes cast at the election of Feb. 22, and issued certificates of election to Jacques W. Johnson, probate judge; Samuel E. Forsythe, sheriff; Marshall A. Garrett, clerk of the board of supervisors; Vincent L. Lane, register of deeds; Robert Robetaille, treasurer; William L. McMath, county attorney; Jacob B. Welborn, county superintendent; Cyrus L. Gordon, surveyor, and George B. Wood, coroner. Rooms in business buildings were rented for the county offices until they were established in the building known as Constitution Hall. From there they were moved to a building on Minnesota avenue, but were changed several times before being established in the brick court-house completed in 1882 at a cost of $35,000.

Although a border county, where both pro-slavery and free-state men strove for control, Wyandotte never took a conspicuous part in politics, yet it was in this county that one of the most important political events in the history of the territory occurred, when on July 5, 1859, a constitutional convention met in the town of Wyandotte and framed the constitution under which Kansas was admitted to the Union.

At the outbreak of the Civil war meetings were held at various points in the county and a number of companies were rapidly recruited. Among them were the Kansas Mounted Riflemen from Quindaro and Wyandotte, and the county was represented in many of the Kansas regiments. During the years of warfare the residents of the county suffered from the raids of organized bands of guerrillas who ran off cattle and horses. Jayhawking on the part of both sides raged through the country and unoffending citizens suffered. The close of the war did not see a cessation of these conditions in Wyandotte county. Murders and lynchings went on for some two years, before the passions aroused by the terrible conflict died away and peace again reigned along the border.

One of the first things accomplished in Wyandotte county after the establishment of the territory was the survey and grading of good roads. The first laid out was that from Quindaro to Lawrence, a valuable highway because it connected two of the most important free-state settlements. It was in good condition as early as 1857. Ferries across the Missouri were established at both Quindaro and Wyandotte in that year. The first bridge in the county was built in 1858 about 3 miles above Wyandotte, the funds for it being obtained by private subscription. In 1859 a territorial highway was established by the legislature from Wyandotte to Elwood in Doniphan county, running through Quindaro, Leavenworth and Atchison. As early as 1857, the people of Quindaro began agitation for a railroad to connect that town with St. Joseph, but the first actual grading for a railroad was done at Wyandotte on the Kansas Valley line in 1859. In 1863 the Kansas Pacific railroad was put in operation through the county along the north bank of the Kansas river. In 1866 the Missouri Pacific was built through the eastern and northeastern part of the county. Since then other roads have been built, all of which diverge, fan-like, from Kansas City to all parts of the country.

The earliest churches in Wyandotte county were the missions among the Indians, established by the Methodists and Baptists. The pioneer Episcopal parish of the territory—St. Paul's—was established at Wyandotte in 1857. The following year the Congregational church and St. Mary's Catholic parish were established. By 1870 several other denominations had perfected organizations and erected churches. The state legislature located the state school for the blind in Wyandotte county, the first building being erected in 1867, in the northwest part of the city then known as Wyandotte. The medical department of the Kansas University is located at Rosedale. The Kansas City University, the Kansas City Theological Seminary and eight Roman Catholic institutions are also located at Kansas City, and Western University, a state industrial school for negroes, is located at Quindaro.

Kansas City (q. v.), originally called Wyandotte, is the seat of justice of the county, and also the largest and most important city in the state. The population of the county in 1910 was 100,068.