I think it’s called a general American accent. I’ve been told that the way people speak in this area.. is the same accent that national news anchors try to mimic. I’m not 100% sure that’s true, but I have heard it more than once.
Edit: (I actually just googled to see if there was a name for this dialect, and I came across several posts that said the same as I posted above. Apparently our accent is very “neutral.”)
I live in Kansas, and I’ve heard that people in Kansas have a nasally sound. Of course, I don’t know it, because I’ve lived here all my life. I do know that when we’ve traveled to other parts of the country people thought we were “southern”.