Watch for the Eb in the chorus. I've seen this song tabbed with a Bm or
Bm7 there. No offense to other posters but it's just not accurate.
Even though Eb isn't in the G major scale, it's used here as a
passing tone between D and E. Play along on just the low E string
and you'll see what I mean. It's part of the walk up D,Eb,Em. 

That being said, I know a lot of players fear the dreaded Eb
chord but this one is a bit easier. It's actually an Ebaug5 and it's fun
to play once you get the hang of it. It sort of a spread out bar chord. 
The index finger bars the 4 bottom strings, 1st fret and the pinky bars bottom
3 strings, 4th fret. Let your index finger ride a touch high and mute the A string. 
And let your pinky mute the high E.

The first part of the intro repeats just before the outro/vocal
vamp...the Ebaug5 shows up once here also.

Ebaug5	XX144X
Cadd9	X32033

Intro
 G                  G       
-7---7-- 7---7---7--3----------3----------3----------3--------
--8---8---8---8-----3----------3----------3----------3--------
---7---7---7---7------0-0h2-0----0-0h2-0----0-0h2-0----0-0h2--
-----------------------------0----------0----------0----------
--------------------2----------2----------2----------2--------
--------------------3----------3----------3----------3--------


VERSE 1
         G
A couple guys in first class on a flight 
                         Bm
From new York to Los Angeles 

Kinda making small talk killing time, 

Flirting with the flight attendants, 
Cadd9               Am
30,000 feet above, could be Oklahoma, 
G
Just a bunch of square cornfields and wheat farms, 
                     Bm
Man it all looks the same, 

Miles and miles of back roads and highways, 

Connecting little towns with funny names, 
Cadd9                         Am              D
Who'd want to live down there in the middle of nowhere,


CHORUS
              Em                 C
They've never drove through Indiana, 
                G
Met the men who plowed that earth, 
                   D                  Eb
Planted that seed, busted his ass for you and me, 
            Em              C
Or caught a harvest moon in Kansas, 
                  D                      Cadd9
They'd understand why god made those fly over states


VERSE 2
G
I bet that mile long Santa Fe freight 
                         Bm
train engineer's seen it all

Just like that flatbed cowboy stacking 
                    Cadd9
US steel on a 3-day haul
                                Am
Road and rails under their feet, Yeah that 
              D
sounds like a first class seat



CHORUS
       Em            C
On the plains of Oklahoma 
           G
with a windshield sunset in your eyes
       D            Eb
Like a watercolor painted sky
            Em                   C        
You'd think heavens doors have opened
                  D
You'll understand why god made 
          C
Those fly over states

Lead 1
   Em      C       G    D  Eb
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-4/9-11/12/9-11/12/7-2/4/2/4------------
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       Em               Cadd9
Take a ride across the badlands
G 
Feel that freedom on your face
D                   Eb
Breathe in all that open space
       Em            C
Meet a girl from Amarillo
                  D
You'll understand why god made
                      C 
You might even wanna plant your stakes
             G (Intro Lick)
In those fly over states 


Outro/vocal vamp
 Em              C       G        D 
  ----------------------------------------
  ----------------------------------------
  ----------------------------------------
  -4-5-4-2-0-2-5-----4-5-2-0-0------------
  ---------------3-3-----------0-2-2-0-0--
  ----------------------------------------         

              Em      C       G   D  Eb
Have you ever been through Indiana
           ------------------------------------
           ------------------------------------
           -4/9-11/12/9-11/12/7-2/4/4/2--------
           ------------------------------------
           ------------------------------------
           ------------------------------------

       Em               C       G        D
On the plains of Oklahoma
       ------------------------------------------
       ------------------------------------------  
       ------------------------------------------
       ---------------------4-5-2-0-0------------
       -------------------------------0-2-2-0-0--
       ------------------------------------------

         Em      C       G       D
Take a ride.....
      ----------------------------------------
      ----------------------------------------
      -4/9-11/12/9-11/12/7-2/4-4-2-2--------
      ----------------------------------------
      ----------------------------------------
      ----------------------------------------