Top 1 percent’s share of income between 1979 and 2007.

In each state in the nation, the top 1 percent of earners saw its share of the income pie grow between 1979 and 2007, according to a new 50-state study of income inequality. The change was starkest in Wyoming, where 9 percent of income belonged to the top 1 percent in 1979. By 2007, that top slice of earners laid claim to 31 percent of all income.

It hasn’t always been the case, though. As the GIF above and graph below both show, the top 1 percent saw its share of all income shrink between 1928 and 1979. Over that half-century, the income pie was shared a little more equally. But since 1979, that trend reversed in every state, according to a new study from the Economic Policy Institute, a think tank that focuses on the needs of low- and middle-income workers.

The authors of the report borrowed the methodology of economists Emmanuel Saez and Thomas Piketty, a duo renowned for their research into income inequality. To get the income data in each state, they analyzed tax data from the Internal Revenue Service. Using that data — which include the amount of income and the number of taxpayers in each bracket — they extrapolated how it would break down along a distribution. They then used state Census data and Piketty-Saez national estimates to identify how to apply that breakdown to each state.

In four states, the only residents who saw their incomes grow from 1979 to 2007 belonged to the top 1 percent, according to the study. (Those states were Nevada, Wyoming, Michigan and Alaska.) In 15 other states, the top 1 percent captured between half and 84 percent of all income growth. That inequality was smallest in Louisiana, where the top 1 percent accounted for just 25.6 percent of all income growth over those three decades.

The data are in line with national estimates. Over that same period, the top 1 percent of households saw income grow by 275 percent, according to a nonpartisan Congressional Budget Office study. The bottom fifth of households, meanwhile, saw income gains of only 18 percent over that time.

And the trend has been continuing, according to EPI. Between 2009 and 2011,the top 1 percent captured between half and all income growth in 33 states, they found. In all but seven of those states, a rise in incomes for the top 1 percent was matched with a decline for the bottom 99 percent.

To view shifts over time, hover your mouse near where 1928, 1979 and 2007 fall on the timeline and wait for the graph to update.