If its wet all year its got to be some sort of ground water.
If it were me, I would start by figuring out where I can get the water to exit the property.
After that I would work up my game plan on how to do it..
If its the whole front yard, I would run a main drainage line through the center of the yard, then run smaller branches off of the main line to collect the water.
Another thing I would do, is after you get you drainage system in place, back fill and do a rough finish grade. Then wait a week. After the week wait is over, go back in and see if there are any other wet areas.
But, with out knowing where you can run your water to, it might be all for nothing.