Are the fairgrounds hosting the July 4th celebration this year?

Yep

Yes. Information can be found here: http://www.statefairpark.org/events/2019/yakima-4th-of-july-celebration. It begins at Noon.

Yes, it may not start until 4pm this year though.

Yes they are. There was talk of not going to, but they are. The carnival rides start on Wednesday.