There may be a few Huns in South Dakota but they are few and far between. Too few to actually specifically hunt them. You may bump a small covey while pheasant hunting but that's your only chance. Many years ago it was quite common to run into to covey but it's been a long time since I've seen a covey of Huns.
Much of South Dakota has turned into corn and bean country, that is not conducive to Huns in particular or pheasants either in general.
I grew up in South West Minnesota, graduating in 1976. I hunted Hungarians literally every day of the season after school from the time I got my drivers license till I moved out of state. This was primarily corn, bean, and hay/pasture ground, with row crops predominant on the landscape. There literally were millions of them in Southwest Minnesota back in those days.(and Im assuming northwest iowa and south east south dakota) . I dont think its a corn/bean factor, but moreso of how todays corn and beans are farmed compared to back then. I think they did very well in the days of the moldboard plow, not so much today.
When we had Huns we mostly grew small grains with a little corn, now it is corn and beans and a lot of grass has turned into corn and beans. I wish I knew what the reason for their decline is.
Loss of habitat, pesticides/herbicides, & predation. My opinion, DDT was a major factor. Thin egg shells couldn't withstand it & nest success took a dump. Other pesticides/herbicides resulted in far fewer "weeds" & bugs. No food. There's a lot less alfalfa & oats & stuff like that planted today than there was 50 years ago. That's what they liked. Gone.