Here is unionization history by state, 1964-2013, using data from UnionStats.com.
Specifically, from (at least I think this is the citation I'm supposed to use) Barry T. Hirsch, David A. Macpherson, and Wayne G. Vroman, “Estimates of Union Density by State,” Monthly Labor Review, Vol. 124, No. 7, July 2001.
The D3 code for the chart is taken from Shan Carter and Kevin Quealy's New York Times chart "Housing's Rise and Fall in 20 Cities", adapted slightly to the different format of the union data, and to only use what I wanted to replicate.
I'd change the colors, but they do work well.
Also thanks to this how-to, by Scott Murray, on making the axes look nicer.
As the scatterplot below indicates, the decline in union membership has been pretty consistent across different states.
A few states stand out for having higher current union membership than expected based on 1964: New York, Hawaii, Alaska, Rhode Island. See what their trends look like in the above chart.
Hawaii is the only state to have a slightly higher unionization rate in 2013 (22.2%) than in 1964 (21.7%).
A few other states stand out for having lower current union membership than expected based on 1964: Indiana, Idaho, Utah.
In particular, Indiana has had the largest 1964-2013 decline in union membership of any state: from 40.9% to 9.4%.