Eureka, the county seat and largest town in Greenwood County, is located south and a little west of the center of the county on the Fall River. The town was founded by the Eureka Town Site Company in 1857 and named for the Greek expression Eureka, meaning "I have found it".
The first building erected was a schoolhouse made of short planks hewn from logs and roughly finished. The building also served as a church and a place for public meetings. At this time the nearest post office was near Burlington, in Osage County, and mail for Eastern friends had to be sent by the chance hand of overland travelers. However, in August, 1858, Eureka gained its own post office, with Edwin Tucker as postmaster.
At the start of the Civil War, Fort Montgomery was built in summer 1861 by local citizens for protection against Indian attacks and Confederate guerrilla forces. It was named in honor of Colonel James Montgomery, a Free-state leader. The fortress was a solidly built large rectangular building with gun whole windows, surrounded by layers of green logs covered with earth up to the level of the gun holes. A small cannon was mounted outside it was commanded by a local farmer named Leander Bemis, but, was sometimes occupied by local militia and government scouts. In 1861, when Eureka’s school burned, classes were taught at the fort.
There was no store in Eureka until after the war; the wooden school house was replaced with a stone building. Among the first business and professional men were: Dr. Reynolds, the first physician; McCartney, blacksmith, 1866; Judge Lillie, the first lawyer, 1868; Hawkins, the first carpenter, 1867, and Mr. Akers, who was the first landlord of the company hotel. Unfortunately, Dr. Reynolds, drowned shortly after he arrived in the Cottonwood River. A few years later, he was succeeded by Dr. Tutton, who located here in 1868, and remained a few years. The first birth in the town was that of Clarence Stoddard, who was born in May, 1869; the first death, Mrs. Mary Stoddard, the mother of this child.
An EF2 tornado struck Eureka on July 7, 2016 at 9:45pm. Over 143 total structures, including at least 50 homes, businesses, nursing home, and grain elevator were damaged. No persons were injured.