Riley County, one of the counties organized by the first territoriai legislature in 1855, is the second county east of the 6th principal meridian, the second south from Nebraska, and the fifth west from the Missouri river. It is bounded on the north by Washington and Marshall counties; on the east by Jackson and Shawnee; on the south by Wabaunsee and Geary, and on the west by Geary and Clay. As originally organized its eastern and western boundary lines were almost identical with those of Marshall county extended south, and the southern boundary was the Kansas river. Between the years 1857 and 1873 several changes were made in the county lines. The eastern line was moved west to the Big Blue river; the western 8 miles west to the present location; Geary county was enlarged from Riley county territory, and additions were made to the latter from Wabaunsee and Geary, forming one of the most irregularly shaped counties in the state.

The first white man to settle in the county was Samuel Dyer of Tennessee, who operated a government ferry at Juniata on the Big Blue river, a few miles above the present city of Manhattan, in the latter part of 1853. The next year Rev. Charles E. Blood of New Hampshire came to Juniata and began his missionary labors. In the same year Thomas Reynolds settled in what is now Ogden township. His house was used as a polling place for the first election, which was held in that year, when 40 votes were polled for delegate to Congress, the majority of them for the free-state candidate. Among those who came that year were: John, James, Patrick and Thomas Dixon, in Ogden township; John M. McCormick, C. P. and John McDonald and William Wiley, in Zeandale township. The settlers of 1855 included N. B. White, Dr. E. L. Patee, William Stone and E. L. Foster, in Ashland township; C. M. Dyche, S. B. White, Jacob Thierer, John M. Morris, Daniel Mitchell and D. L. Chandler, in Ogden township; Daniel S. Bates, a Mr. Morse, John C. Mossman, J. M. Burleigh and J. H. Pillsbury, in Zeandale township; Henry Coudray and family, S. D. Houston and a man named Eubanks, in Grant township; Gardner Randolph and sons in Jackson township; J. P., Jonas, and T. R. Hair, Maj. Abram Barry, Marshall Barry and George Taylor, in Madison township; and the delegation which comprised the Manhattan town association, in Manhattan township.

A number of historic roads came through Riley county. Col. John C. Fremont on his second expedition in 1843 followed the water courses to the present site of Ft. Riley. The Leavenworth and Pike's Peak express crossed the county by way of the fort, which was also a station on the Butterfield Overland Despatch route, and the south branch of the California trail ran through by Manhattan.

The county derived its name from Fort Riley (q. v.), and the first capital of the territory was at Pawnee, just east of the military reservation 2 miles from the fort, where the old building used as the first capitol still stands. Dr. William A. Hammond, Capt. Nathaniel Lyon, Robert Klotz, Robert Wilson, and several others had settled there before the legislature met on July 2, 1855. (See Reeder's Administration.)

On the organization of the county the legislature elected the following officers: John T. Price, sheriff; Clay Thomson, probate judge; Thomas Reynolds and William Cuddy commissioners. When the court convened John S. Reynolds was made clerk. The county seat was at Ogden, where a provisional court-house was rented. Preparatory to the election to choose a permanent county seat four precincts were established in Sept., 1857—Randolph, Manhattan, Ogden and Montague. The contesting towns were Ogden and Manhattan, the former receiving a majority of 31 votes. Later fraud was proven and Manhattan became the county seat. The next legislature passed an act making Manhattan the permanent county seat and authorizing and requiring the county officers to move the county records to that place before the first Monday in February following the passage of the act. At first there were but four townships, Manhattan, Ogden, Pierce and Dyer. Numerous changes occurred until the county assumed its present form in 1873, when there were nine townships—Jackson, May Day, Bala, Madison, Grant, Ogden, Manhattan, Ashland and Zeandale. At present there are fourteen townships, Center, Fancy Creek, Sherman, Swede Creek and Wild Cat having been added.

Some of the first postoffices in the county were Ashland, established in 1853, M. D. Fisher postmaster; one in Zeandale township, about 1857, D. M. Adams postmaster; Stanton, in May Day township, 1869; Ogden and Riley Center. Among the early marriages were those between C. P. McDonald and Mary McCurdy of Zeandale township; Thomas Dixon and Mary Hoffman in Ogden township; James Johnson and Mary A. Hair in Madison township; Lewis Baldwin and Matilda Randolph of Jackson township; William Frake and Catherine Condray of Grant township, all in 1856. The first births were those of Ernest McCurdy in Zeandale township and Alla Mobley in Ogden township the same year, and the first death was that of John Dixon of Ogden township in Aug., 1855. The same summer a number of deaths from cholera occurred at Fort Riley. (See Cholera). The first schools in the county were at Manhattan and in Ashland township in 1857, Miss Marcia Woodward teaching the latter. The next year a school was opened in Zeandale township, Grant and Ogden townships following in 1859.

The area of the county is 617 square miles, or 394,880 acres. The surface is generally undulating, except for the limestone bluffs along the Blue and Kansas rivers, which form the eastern and southeastern boundaries. There are several smaller streams, of which Fancy creek flowing from west to east across the north, and Wild Cat creek flowing southeast across the central portion are the most important. The bottom lands along the streams constitute about 20 per cent. of the total area. Magnesian limestone, cement rock and potter's clay are found in paying quantities. The principal farm products are corn, oats, hay, wheat, Irish potatoes, rye, alfalfa, live stock and fruits. The total value of farm products in 1910 was $3,761,102, of which corn amounted to $1,107,348 and live stock to $1,699,666.

The county is well supplied with railroads. The Union Pacific, which was the first line built, follows the Kansas river to Manhattan, where it crosses the Big Blue and runs southwest into Geary county. The Blue Valley branch of the same road diverges at Manhattan and follows the Big Blue, running first northwest, then northeast into Marshall county. The Chicago, Rock Island & Pacific enters south of the Kansas river and goes west to Manhattan, thence northwest into Clay county. The Leavenworth, Kansas & Western branch of the Union Pacific crosses east and west near the center. The population of the county in 1910 was 15,783, a gain of 1,955 during the preceding decade.