I am assuming that you can see the new growth peaking from the soil. I would dig up about half the plant leaving the rest undisturbed. This is so that if the divisions don't take then you will at least still have the mother. The number of new plants you can get will depend on the number of new shoots there are. I would try to keep 2 or three shoots per division although technically each one could become a new plant on its own. Having multiples in each clump will help the survival rate of each clump. Tarragon won't start growing until the days get longer. The divisions might take better once they just start to grow.
If there aren't any new shoots peaking out then don't divide yet.

Thanks for the advice. We are still a month and a half away from the beginning of spring. I will heed your directions! Thannks again.