In general the 1920s were the high point of membership and power of the KKK, although from the beginning of the decade to the end there was a decline, so the answer would be both true and false, although in general they were quite powerful during the entire decade. It's important to understand that the Klan of the Reconstruction era was not primarily a racist organization, and that in fact former Confederate General Forrest disbanded the Klan because of the racist activities of some members. The Ku Klux Klan of the 20th century is a purely racist organization with no actual ties to the original group. The membership of the Klan, at its peak in the mid-1920s, has in the modern era always lived primarily in Ohio, Michigan and California, not the Southern states.
This question is both true and false. It is true that the Ku Klux Klan gained a great deal of power in the mid 1920's. They had as many as five million members. In the early 1900's there were many southerners moving north because of industrialization. Note that many of these people were not white and not Christians. It was during this time that a second klan was formed with a new agenda in mind.
So by the time the 1920's arrived, the Klan had millions of members. It is very important to note that by the very end of the 1920's, the number of members in the Ku Klux Klan had dramatically dropped due to opposition that the klan received from the public. Soon after, the Depression and World War II made their numbers decline even more.
The statement is false. Klan membership grew more rapidly during the 1920's than it had from its inception in 1865 and has declined since the 1920's. Between 1920 and 1925 there were approximately 4 million members in the Ku Klux Klan. The Klan had expanded its African American racist agenda to include an anti-catholics, anti-semitism, and immigration from just about anywhere.
This statement is false. The KKK actually came back to power in the 1920s. It had essentially been dead from the time that Reconstruction ended. But then it came back to life again during the 1920s.
There are some strange things about this KKK revival.
First of all, much of its power was in the North rather than in the South where we always think of the KKK being centered. They even had one of their members who became the governor of Indiana.
The other strange thing is that the KKK was not really anti-black at this point. Instead, they were mostly opposed to immigrants, Jews and Catholics.