This is undoubtedly a Tussock moth, (family Lymantriidae), is she not gorgeous? But be careful, some of them can pack quite a punch from the stinging hairs - yes, I know someone who stepped on one barefoot, and had to go to hospital!
The common name for this animal is (doh) derived from the hair tufts, or tussocks, found on most larval forms.
Most caterpillars of this species feed on the foliage of trees and shrubs, sometimes foraging daily from a silken tent or colonial nest of webbed leaves. Here is one I found at the end of May...the others were in late June.
YOu may have seen their large cocoons on trees, as pupation occurs aboveground in cocoons attached to tree branches or trunks.