I'd say the question is a bit vauge.
While my knowledge is limited to what I've seen in irrigation and plumbing forums, I don't think I've ever seen any code related issues saying where you have to put check valves, especially since the main location I've seen check valve being located (in relation to irrigation) is in latteral lines so that the water left in the lateral lines doesn't flow backwards and out of the lowest head (for example, I'm seen check valve that are ment to be installed at the inlet of the sprayhead, effectivenly sealing all the water in the latterals because there's no where for air to get back into the system to allow the water to flow out.
So the only general answer I can say is to make sure the placement of what ever check valve you are talking about is located in such that you can blow all the water out of the pipes at the end of the year when you winterize. Of course the other thing is that that port (input) you use to blow out the system has to (based on plumbing codes) must be located AFTER a backflow preventer that seperates domestic water supply from irrigation supply (and a single check valve is NOT a backflow preventer... not in a plumbing code scence).