Unfortunately no, the Klan is not gone. At the time the novel is set in it was in one of the low-profile periods in much of the South. The Ku Klux Klan was originally a social organization founded in 1866 in Pulaski, TN, a fraternity of university graduates which had private meetings and did social works, and one of its rules was that members were required to wear disguising robes and hoods when appearing in public as members. As time went by it expanded and gradually accepted other chapters. Some of the members took to riding in the countryside at night scaring people, both black and white, but this was frowned upon by the general membership. As the occupation by Union troops and the depredations of the "carpetbaggers" and "scalliwags" (not to mention the bureaucratic control by military government) under the Reconstruction era grew, these Klan groups banded together under the leadership of former Confederate General Nathan Bedford Forrest as a political resistance group. Although Forrest was himself a believer in the superiority of whites, he disbanded the Klan when members complained of Klansmen terrorizing blacks as if it was an official Klan activity.
The Ku Klux Klan was defunct for awhile, but as the "Jim Crow" era deepened late in the 19th century it reappeared. Ironically, the segregationist legislation began under the Republican state governments following the war, but kept getting worse throughout the South and West. The true era of Jim Crow didn't really get underway until the 1880s and 1890s, with miscegenation and segregation laws beginning to spread throughout the both South and the rest of the nation. By the start of the 20th century the Klan was fully revived, and formally reconstituted by W.J. Simmons in 1915. The Klan continued expanding through the 1920s, until well into the recovery period of the late Depression. At that time, and since, the vast majority of the Klan's membership lived in Michigan, Ohio and California.
A further recurrence occurred in the 1960s during the Civil Rights Movement era, and although incidents in the South achieved most media attention the Klan membership, funding and majority of activities occurred in the North and on the West coast. There were three major organizations by the 1970s, including the Invisible Empire, United Klans of America Incorporated and a third group allied to the American Nazi Party. Although these sorts of organizations are still with us, the KKK per se is fragmented, and their membership has been in a continual decline for decades. There are other such groups, however, the largest of which is the Aryan Nation.
One of the best places to get information on these groups is the Southern Poverty Law Center, for which there is a link below.