The farthest north I have physically seen rows of palm trees is San Jose, CA, USA.
San Jose, CA, USA. ~Latitude:N 37° 20' 21.7885", Longitude:W 121° 53' 41.8398"
I have lived and traveled within Washington and Oregon states and I have not seen the rows of palm trees that are prevalent in Californian landscaping--the planting of rows of palm trees along streets and boulevards is especially popular in Southern California, Los Angeles area, and further south. In San Jose, CA, some developers have tried to mimic the palm tree landscaping which is prevalent in Southern California.
I think the majority of the palm trees planted and used in today's San Jose, CA landscaping were planted around the Dot Com boom days of the late 1990s back when developers had money to burn; I do not remember seeing many palm trees being brought into the city before 1995 or after 2000. Basically, what happened, after the Dot Com crash in 2001, many developing projects buildings, landscaping, etc., were suddenly and simply abandoned for a long time. Anyway, I always thought the San Jose palm trees looked a little odd, and I think that compared to the palm trees in Southern California or Hawai'i, San Jose's trees look too thin and sickly.
I have not seen single palm trees just growing wild in Washington or Oregon either; Washington and Oregon are temperate, not tropical rainforests; we have the water to grow palms, but not the heat and sun necessary to keep the trees alive.
Also, I have not seen palm trees very much or at all in the Southwest (AZ, NM, UT), Rocky Mountains (ID, CO), nor Midwestern United States (NE, IA, MN) in my travels. I am sure there are palm trees in Nevada and Arizona, I have seen the trees occasionally, especially as part of major city landscaping, but not so much in the rural communities; it would take too much water to keep the palms alive in the arid desert environment, plus there is the whole issue of planting in caliche soil (basically, the ground has to be jackhammered, which is a hassle, etc.).