This list is for fun and not every lookout has been added that existed prior to 1920. I am just adding more as I come across them. I have not gone through all my trip reports and checked. Some of the dates are based on research I was not part of. I cant verify the accuracy of all dates.
Washington Lookouts
Early Fire Lookouts in Washington - The 1920 List
Locations known to be used in 1920 or earlier
Camp in 1914, cabin in 1920
Northeast Cascades
Region
What was there
Location
North Olympics
South Cascades
Camp in 1917, structure started in 1917
Mt. Rainier area
Structure built in 1916
Willapa Hills
Structure built in 1919
Camp in 1915
Northeast Cascades
Crows Nest tree in 1911, log cabin below
West Central Cascades
North Central Washington
Northeast Washington
Camp in 1920
Camp in 1918
Camp in 1912 with stone shelter, 1914 log cabin
South Olympics
Northeast Cascades
East Central Cascades
Camp in 1914, structure built in 1920
Structure built in 1916
Crows nest in 1914
Camp in 1916
Northwest Cascades
Northwest Cascades
West Central Cascades
East Central Cascades
Camp on or before 1916, structure by 1920
Camp in 1915
Camp in 1916
South Cascades
North Olympics
Structure built in 1917
Structure built in 1917
Considered
South Cascades
Central Cascades
Northeast Cascades
West Central Cascades
Northwest Cascades
South Cascades
East Central Cascades
Mt. Rainier area
East Central Cascades
East Central Cascades
East Central Cascades
East Central Cascades
East Central Cascades
Crows nest tree 1918 or prior
Camp in 1920
Camp in 1917, structure built around 1920
Camp in 1916, structure built in 1919
Camp in 1910, structure built in 1913
Camp in 1918
Cupola started in 1918
Camp in 1914
Camp in 1914
Camp in 1914
Camp in 1914
1919 in Report of the Director of the N.P.S.
1918 feasibility team visited summit
Aeneas Mountain Lookout 1920ish
Mount Adams Lookout 1921
Anvil Rock Lookout 1919
Buck Mountain cabin 1920
Calispell Peak Lookout 1923
Dirtyface Peak Lookout camp 1920
Finley Peak Lookout 1920
Kloshe Nanich Lookout 1918
Red Mountain Lookout 1910
Granite Mountain Lookout 1920
Boisfort Peak Lookout 1918
Mt. Pugh Lookout camp 1917ish
Mt. St. Helens Lookout 1921
Mt. Pilchuck Lookout 1921
Kiona Peak Lookout 1917
Tip Top Lookout camp 1915
Jumbo Lookout camp 1916