Last autumn I read Timothy Egan’s masterpiece, “Fever in the Heartland,” which covers the abrupt rise and fall of the Ku Klux Klan in Indiana. It sent me down a research pathway that uncovered ill-effects of the KKK on population and demographics that still plague parts of Indiana.

I expected this book to be a difficult, maybe even painful, read. I could not have been more mistaken. It was as delightful book as I have read in years. “Fever in the Heartland” transports the reader to Indiana in the early 1920s. Egan fleshes out the meteoric rise of the Indiana KKK from complete absence to a full third of native-born men in fewer than five years.

There were plenty of villains in the tale. Villainy is the hallmark of the Klan. But, there also were grifters who promoted the Klan’s hateful ideology because it paid very, very well.

The story also has resolute heroes. These include a Muncie newspaperman who hounded the KKK, despite frequent beatings, and a grizzled Civil War veteran who reminded folks from whence the Klan came. Egan also weaves in tales about Hoagy Carmichael and Louis Armstrong, as well as many otherwise unknown folks who faced down the Klan.

The apex of the story is about the violent rape and torture of a young woman, Madge Oberholtzer, by D.C. Stephenson, the state KKK’s grand wizard. Oberholtzer died, but not before giving her testimony. Stephenson was convicted of murder by a prosecutor and jurors who faced death threats.

Egan’s book prompted me to ask questions about the long-term effect of the Klan in counties where it was most active. That led me on a six-month quest.

The first thing to know about the KKK in Indiana is how large and widespread it was. Indiana had the highest share of residents in the Klan at any time in history. We also had the largest Klan gatherings and parades anywhere in history. But the Hoosier Klan was different.

Indiana was a staunchly Union state in the Civil War, whose veterans were only as far removed from that conflict as Vietnam War vets are today. Indiana was still a fledgling manufacturing state, with few immigrants, and a tiny share of African-American or Jewish residents. Catholics were only 10.5 percent of the average county population.

Hatred didn’t bubble up from the population. It was a manufactured commodity. Most scholars of the period argued that populism resulting from rapid economic change fueled the Klan movement. Grifters like Stephenson merely rode the wave of opportunity. They sold hate and cowards robes at a hefty profit.

A decade ago, two well-known economists, Roland Fryer and Steven Leavitt looked at the effect of the KKK on voting patterns, immigration and African-American migration. They found that heavier Klan presence reduced the growth of immigrants and African-Americans. But they looked only through 1930.

I wanted to look very long term. My interest was in the effect of the KKK on the Jewish, Catholic and African-American population, as well as overall population growth. I also surmised that the best way to measure the Klan was not to look at the proportion of residents who joined.

Egan and many scholars before him noted that most people joined without any real ideological attachment to the Klan. Membership was expensive, $175 in today’s dollars, but there was substantial coercion. A violent local Klan might not boost membership, and remember this was first and foremost grift and greed.

Moreover, the secrecy of the Klan meant that prospective members could be easily misled about its numbers. A better measure of the KKK’s intensity was how heavily they were covered in the newspapers.

We have numbers of members for 90 out of 92 counties from another book by Leonard Moore, and Virginia Commonwealth University compiled data on the presence of a Klavern (a local organization) in 75 counties. But, in a quarter of counties, the Klan was so active they had their own proper name. Examples of these are the Mystic Tie, Anthony Wayne, and the Vale of Paradise Klan.

I wrote a statistical model that tested the effect on population before and after the Klan. Because we have a clear before-and-after test, we can evaluate whether the Klan’s presence caused population changes. Using data from the Census and the Association of Religion Data Archives, I analyzed the effect of KKK share of the population, number of Klaverns and number of named Klaverns.

All of these had long-term effects on Indiana. For example, a single named Klavern in a county reduced the average number of Catholics by 6.2 percent, or equivalent to 1 in 16 Catholics.

The effect on the Jewish population is even larger. A single named Klavern in a country reduces the Jewish population by nearly 1 in 4 residents. That was the average effect of the Klan on these groups from 1930 through 1990, the last year of the religious data. That is stunning.

The African-American share of the population isn’t readily available for all these years. But the number of named Klavern’s per capita explains a whopping 68 percent of the variation of African-American residents in our state in 2010. The overall population effects were even larger.

I also found that having a single named Klavern reduced population in the typical county by 4,150 residents 25 years later. This is about 0.5 percent of the total, with effects extending to at least through 2010.

Finally, I wanted to know if having Klan presence affected long-term quality of life. My interest in this was raised by a 2019 study in which my colleagues and I stumbled upon the national headquarters of the KKK. We wanted to conduct research visits to places that had much higher or lower quality of life than their mix of amenities predicted.

One small county was a huge outlier. Although teeming with amenities—great climate, rolling hills and lakes, a local college—it had unexpectedly low quality of life. That was because it also had the national headquarters of the KKK.

That prompted me to test the effect of the KKK on quality of life. I found that having a Klan presence even 50 years ago is more damaging to quality of life than an EPA superfund site, near-Arctic climate or bottom-tier schools. That is a costly legacy of ignorance and hate.

There is a lot to glean from Egan’s splendid book, including some echoes of today. Grift, rape and populism aren’t new. But, my follow-up analysis finds two things worth knowing. First, if you tell folks they aren’t welcome, they likely won’t come. Second, whatever may have caused Hoosiers to join the Klan—hate, fear, coercion or money—the KKK has been good at one thing only. It has helped keep places poor for a century, weakening local economies, reducing population growth and diminishing prosperity.