I've seen whitetail 2 times in the past 10 years near my place in Snohomish. Once saw about 5 crossing Lowell Larimer Rd. halfway between Seattle Hill Rd. and Lowell, and once 3 crossing Welch Rd. just up from High Bridge. The whitetail flag tails were unmistakeable. No idea how the got there, or how long they've been there.