Kona cotton is actually a brand of 100% cotton fabric, produced by Robert Kaufman. From what I'm able to gather, it has a 60 by 60 thread count -i guess per square inch- and is considered a premium fabric. Its quite affordable, well in my shop it is, and if I need a solid, its what I grab.
I've used it for the last while and I love it. Great texture and shrinkage is very minimal, however it can vary, depending on how you wash it. Last time I preshrank some white, I threw it in the wash with my white laundry -socks, underwear that type of thing- and there was no noticeable shrinkage at all, used the bleach cycle, even threw in bleach!