Final answer:
The largest organization in Indiana outside of the Southern states in 1922 was the Ku Klux Klan (KKK), with an estimated membership of 350,000. However, due to scandals and outspoken opposition, the Klan's membership declined drastically.
Step-by-step explanation:
The organization in Indiana that boasted the largest membership number outside of the Southern states in 1922 was the Ku Klux Klan (KKK).
According to historical sources, the Indiana Klan had an estimated membership of 350,000 in 1922, making it the largest Klan organization in the nation at that time. However, due to scandals and negative attitudes towards the Klan's beliefs, its membership drastically declined to 15,000 by the end of 1926.
It is important to note that the Klan's decline was largely attributed to the efforts of individuals like journalist William Allen White, who vocally opposed the Klan's influence and made it a leading issue in the 1924 race for the governorship of Kansas.