The Tennessee General Assembly established DeKalb County in December 1837 and named it in honor of Johann DeKalb, a German general who died while serving in the American Revolution. The county seat was located on fifty acres donated by Bernard Richardson and named Smithville by the general assembly in honor of Samuel Granville Smith of Jackson County, a state senator and Tennessee's secretary of state. Smithville's population in 1998 was 4,229. A widely attended Fiddler's Jamboree has been held annually on the square on the July Fourth weekend since 1971.
Liberty is the oldest town in DeKalb County. By 1807 it had been laid off in half-acre lots by its founder, Adam Dale, DeKalb County's first settler, who arrived in 1797 from Maryland. Dale, along with John and Leonard Fite and probably Stephen Robinson, cut a road into the Liberty area from Nashville. In 1805 Dale's friends and relatives followed these groundbreakers to the area.
Six miles northwest of Liberty is Alexandria, established in 1820 by Daniel Alexander, another migrant from Maryland. Alexandria prospered and soon contained a number of flourishing businesses and good schools. In 1856 Alexandria hosted the first DeKalb County Fair, which is still held there annually. The fair grandstand is the oldest in the state and is listed in the National Register of Historic Places. Also listed in the National Register is Alexandria's Seay Chapel United Methodist Church, a former African American church building and now a community center, where W. E. B. Du Bois attended services as a young man. Alexandria's 1990 population totaled 730.
DeKalb County furnished almost as many Union troops as it did Confederate troops in the Civil War. Fighting occurred around Liberty in 1863 and included the battle of Snow's Hill on April 3, which engaged about two thousand men on each side. After the armies left, guerrillas, or “bushwhackers,” terrorized both Union and Confederate sympathizers in the county. Bitter feelings about the war lasted for decades and were especially strong at election time. Not long after the war, Dowelltown grew up one mile east of Liberty. Named by the postmaster, Frank Dowell, it became the home of several Union army veterans.
John H. Savage ranks among DeKalb County's outstanding antebellum political leaders. Savage, a Democrat, served in the U.S. Congress from 1849 to 1859. During the Civil War, he attained the rank of colonel in the Sixteenth Confederate Infantry Regiment. His principal political opponent was William B. Stokes, who had served as a colonel in the Fifth U.S. Cavalry and became a Republican congressman in the postwar period.
World War II brought many changes to DeKalb County. The war affected almost every family, as more than 700 area citizens entered active military service. DeKalb Countians on the home front got a taste of military action when the county became the site of army maneuvers held in preparation for the assault on Europe.
Just after World War II Joe L. Evins was elected to his first term and served as a Democratic congressman from 1946 to 1976. State-level DeKalb Democrats have also included McAllen Foutch, who served in the general assembly from 1943 to 1959 and as Speaker of the House from 1949 to 1959 and Frank Buck, a state representative elected continuously since 1973.
From its earliest settlement DeKalb County's economy depended on agriculture, but enormous economic change occurred after World War II. In 1948 the U.S. Army Corps of Engineers completed Center Hill Dam, flooding the Caney Fork area and forcing many farm families to move. By 1995 almost every farm family in the county depended on supplemental income from an outside source.
Some manufacturing occurred in the county in the antebellum period. Jesse Allen operated an iron forge on Pine Creek, and the Lefevre family and their relatives made crockware pottery. Manufacturing on a large scale did not begin, however, until 1948, when a shirt factory was constructed in Smithville. Many of the county's present businesses supply parts for the growing automobile industry in Tennessee.
Electricity became available in the towns in the late 1920s, but rural families did not receive the utility until the late 1940s. Telephone service from the DeKalb Telephone Cooperative began in 1951. There were no medical facilities in 1945, but hospitals and nursing homes began to appear in the 1960s, and now Baptist DeKalb Hospital provides a wide range of medical services to the county.
According to the 2000 census, DeKalb County's population totaled 17,423. At the end of the Civil War, African Americans made up about 10 percent of the population, but out-migration had reduced the number of blacks to less than 3 percent by the 1990 census. In the 1980s a number of Mexican laborers came to work in DeKalb's nurseries, but few have become permanent residents.