Hi Kasie!
I am assuming by your question that you mean the Marathon weekend in January? There are other race weekends that don't have full marathons, so if you mean a different weekend, let me know and I can give you specifics about it!
The parks will operate as usual during marathon weekend. The only day you will really notice and will probably see at least part of the race will be on Sunday. That is the day of the full marathon and runners will still be completing the race up until 1 or 2 o'clock in the afternoon. The parks will still be open, and transportation will still be provided from the resorts, the buses just may take different routes, and you will most likely see the runners out your window!
There will be maps of the courses on the
Walt Disney World Marathon website. They aren't posted yet, but you can find them on the "RUNNER INFO" tab, then under the "Course" tab.
On Sunday, the runners will go through the Magic Kingdom before it is open. The second park will be Animal Kingdom, followed by Hollywood Studios and then finishing at Epcot. So, if you really want to avoid the situation, I would go to either Magic Kingdom or Animal Kingdom on Sunday:)
I hope this helps! Please let me know if you have any other questions.