Alfalfa County is a county located in the U.S. state of Oklahoma. As of the 2020 census, the population was 5,699. The county seat is Cherokee.

Alfalfa County was formed at statehood in 1907 from Woods County. The county is named after both the alfalfa crops grown there and William H. "Alfalfa Bill" Murray, the president of the Oklahoma Constitutional Convention and ninth governor of Oklahoma. He was instrumental creating the county from the original, much larger Woods County.

Indigenous peoples inhabited and hunted in this area for thousands of years. By 1750, the Osage had become a dominant tribe in the area. About one third belonged to the band led by Chief Black Dog (Manka - Chonka). Before 1800 they made the Black Dog Trail starting east of Baxter Springs, Kansas and heading southwest to their summer hunting grounds at the Great Salt Plains in present-day Alfalfa County. The Osage stopped at the springs, which attracted migratory birds and varieties of wildlife, for its healing properties on their way to hunting on the plains. The Osage name for this fork of the Arkansas River was Nescatunga (big salt water), what European-Americans later called the Salt Fork. The Osage cleared the trail of brush and large rocks, and made ramps at the fords. Wide enough for eight men riding horses abreast, the trail was the first improved road in Kansas and Oklahoma.

The treaties of 1828 and 1835 placed what would later become Alfalfa County within the Cherokee Outlet, which was owned by the Cherokee Nation. Ranching became the primary economic activity from 1870 to 1890; cattle companies that belonged to the Cherokee Strip Live Stock Association leased grazing land from the Cherokee. Prominent rancher, Major Andrew Drumm operated the "U Ranch" here as early as 1870. Its headquarters were southeast of Driftwood on the Medicine Lodge and Salt Fork rivers.

Woods County was created in September 1893 at the same time as the opening of the Cherokee Outlet with the Cherokee Strip Land Run. As population increased and Cherokee land titles were extinguished, the legislature authorized the creation of Alfalfa County in 1907, as part of statehood. The county was named after William H. "Alfalfa Bill" Murray, who served as the president of the Oklahoma Constitutional Convention and would later be elected as the ninth governor of Oklahoma. He promoted creation of this county.

The city of Cherokee was designated as the county seat after being chosen by voters in an election held in January 1909. Other towns receiving votes for the honor were Carmen, Ingersoll, and Jet.

Alfalfa County's population was primarily of European-American ancestry. European immigrants and their children were numerous in the early 1900s. Germans from Russia (ethnic Germans who immigrated to American from Russia), many of whom were Mennonites, settled near Ingersoll, Driftwood, Cherokee, and Goltry. Early censuses also reveal a considerable number of Bohemians from the Austro-Hungary Empire. At the turn of the twenty-first century, nearly 17 percent of county residents claimed German ancestry on the census. One Mennonite church (in Goltry) remained as of 2006^[update].

Early railroad construction, from the Choctaw Northern line (1901), the Kansas City, Mexico and Orient (1901), the Arkansas Valley and Western (1904), and the Denver, Enid and Gulf Railroad Company (1904), contributed greatly to the county's early prosperity and caused many small towns to flourish. They would compete as wheat-shipping points and agribusiness centers for many years thereafter. However, by 2000 only one rail line, the Burlington Northern Santa Fe, served the county.