The majority of the population centers in North America are in the East and the region of the Midwest is more or less geographically in the middle of the continent and to the west of the population centers so it makes sense to me that it's the Midwest.
Preaching to their kids about the 'dangers of dating a colored person', in a public space no less, is something I've never witnessed in rural, SW Wisconsin, if that counts as 'midwest'.
Those instances were not public. I was friends and/or extended family with the people that were saying and doing those indoctrination things. The lynching tree itself was not something the father in law told me directly either (my wife told me what he said) but I was around when he lectured everyone on racist stuff. I would listen to other parents explaining racist stuff to their kids in their homes as well.
The open racism was the stuff like the Quiznos where an interracial couple got yelled at for existing and forced to leave, the shouts and hollers that people of color would get for walking down the street, and how openly people would express racial animus at work or in public. At various jobs I had to threaten to get HR involved just to get my coworkers to stop dropping the N-word in every other sentence. This was white guys saying it in racist context out loud. They used the word 10x more than my African American coworkers, who never used it derogatorily as the whites did.
Then you layer on housing discrimination, schooling discrimination and police issues and it was a mess. There is a reason Ferguson happened down the road from where I once lived and worked in the Midwest and there was not an equivalent in the Southern towns I lived in.
But it's not the case that people would stop a rando on the street and tell them about the lynching tree. Well, actually they might if the rando was a person of color as a way of intimidating them. But I would consider that extreme even for where I lived.
For reference, all of these examples are from 2006 - 2016 in two different states (Illinois and Missouri). It's not ancient history and I don't think the racism was a unique feature of the various towns I lived in in these states.