Not counting the incumbent, the two most recent governors of Illinois are currently in prison.
Have any of the other 49 states had two former governors in prison at the same time? Bonus points if they were the two governors from two consecutive terms (like Illinois’).
It appears that we’re the first. According to this Washington Post story, only two other states (Louisiana and West Virginia) have had two incarcerated governors, ever. (Illinois has had four.)
The two from Louisiana (Richard Leche and Edwin Edwards) and the two from West Virginia (William Barron and Arch Moore) were decades apart, and didn’t do time at the same time. So, we’re #1.
However, Maryland deserves honorable mention, in that two consecutive governors, Spiro Agnew and Marvin Mandel, were felons. Agnew, of course, was able to avoid the risk of prison time by offering his resignation from the Vice Presidency. Mandel did 19 months in 1980-81, although his conviction was later overturned.
Well, see, pensions are always an iffy thing in Illinois. We’re just making this our retirement plan for governors. 
Arizona comes close.
In 1988, Evan Mecham (“While governor, Mecham became known for statements and actions that were widely perceived as insensitive to minorities. Among these actions were the cancellation of the state’s Martin Luther King, Jr. Day, attributing high divorce rates to working women, and his defense of the word “pickaninny”, in describing African American children.” to quote Wikipedia) was impeached for his actions in relation to a large, unreported campaign contribution. He was, however, acquitted of felony charges.
Fife Symington was convicted of bank fraud in 1997 and automatically removed from office.
Barron was governor from 1961-65. Moore first served in 1969. Not consecutive, but not decades apart. Moore was later elected in 1984 for a 3rd term as Governor and it was from this later term that his conviction arose.
So, yes and no on the “decades apart.”