This is how random my mind can be.
Today, I saw someone on Facebook mention polka dots, which led me to ask myself, "Why are they called polka dots anyways?" So, I did what any self-respecting, smartphone-owning individual would do -- I Google'd it :)
The answer is as clear as Mississippi Mud. The one thing that IS clear is that it has nothing to do with Mississippi.
After reading several "answers" from a variety of sources, I am still not clear that the name has anything more to do with it than the fabric pattern just happened to be introduced in the height of the polka dance craze in the mid-1800's, so someone started calling them polka dots and it just caught on. Seriously !!!
Short answer -- no one seems to really know.
Read for yourself -- here's the references I used: