I will paraphrase a generous sportsman who replied here to a similar query a few years ago. "Go to Coronet bay and drive to the end of the servicable road. Park and walk the quarter mile to the end of the road. Fish there."
A couple other nice places are South Island State Park, and Fort Casey State Park. Harvey Manning said something like, 'Look West from Fort Casey and that is China just over the horizon.' If the wind is blowing don't go to Casey. You may pick up a salmon or Searun Cuthroat.
I don't know if there are winter run Steelhead on Whidbey, I doubt it. The beaches I mention are known for a few summer runs in the fall. There are a couple of good lakes to fish, but I don't know whether they are open, and I have not fished them. I suspect someone who knows more about that will chime in.
No winter steelhead native to Whidbey Island. The ones taken in the surf during the winter are Skagit, Sauk and Stillaguamish fish. They should probably be left alone since those runs are so drastically depressed.