A good interactive graphic at NPR showing the change in union membership for each state from 1964 to 2014.
The overall rate has fallen from around a third to under 10%.
The three most unionised states today are New York on 25%, Alaska 23% and Hawaii 22%.
24 states have a union density of 10% to 20%.
16 states have a density of 5% to 10%.
Eight states have a union membership rate of under 5%, with the lowest being North Carolina at 2%.
The biggest declines over 50 years have been Michigan and Indiana which have both had 30% drops.
The only state to increase is Hawaii from 21.7% to 21.9%.
Would be interesting to explore why some states have declined so much, and others have not.