From the Alan Lomax/Moses Asch "Leadbelly Songbook," here are the basic progressions. Both of these songs are written out in A.

DeKalb Blues
[A]DeKalb blues, Lord, makes me feel so bad [A7]
[D7]DeKalb blues, Lord, makes me feel so [A] bad
Just to [E7] think about de [D7]times I once have [A] had.

Rock Island Line
chorus
[A]Oh the Rock Island line is a mighty good road
Oh the Rock Island Line is the [B7] road to [E7]ride
If you [D7] want to ride it got to ride it like you find it
Get your ticket at the station on the [E7] Rock Island [A] Line.

verse
[A]Jesus died to save our sins
[E7]Glory to God we're gonna [A] need him again.