I work in the National Guard as an officer.
I joined back in 98'  we are part of the reserve components of the United States Armed Forces.
Can you have a civilian job while serving in the National Guard?
You can but you still have to report. National Guard units are under the dual control  of the states and the feds.
I see, and where does the National Guard operate?
We are stationed all over the U.S! he National Guard is a joint activity of the United States Department of Defense (DoD) 
Have any US presidents served on the National Guard?
Im not sure actually. But I have learned that composed of reserve components of the United States Army and the United States Air Force: the Army National Guard.