I'm sure there are many more country songs about Oklahoma, but here are the ones I can think of off of the top of my head:
"Oklahoma"....our state song of course
"Okie from Muskogee" Merle Haggard (the best song in the WORLD)
"Take Me Back to Tulsa" Bob Wills
"That's When Country Comes to Town" Toby Keith
"The Day that She Left Tulsa" Wade Hayes
"Oklahoma Hills" Woody Guthrie
"Chasing Those Texas Plates....'just three Oklahoma girls'" Kelly Coffee
"Oklahoma Rising" Vince Gill
"A Little White House on the Oklahoma/Texas Line" Rascall Flatts
"Tell Me Something Bad About Tulsa" George Strait
"Big 'Ol Truck" Toby Keith
"Tulsa Time" Don Williams
"You're the Reason God Made Oklahoma" David Frizzell and Shelly West
"Oklahoma Swing" Vince Gill and Reba McEntire
"Boys from Oklahoma" Cross Canadian Ragweed"
"Oklahoma Breakdown" Stoney LaRue (a must listen if you've never heard)
"Good Old Oklahoma" Bob Wills
"I Ain't In Checotah Anymore" Carrie Underwood
"In Oklahoma" Cross Canadian Ragweed
"If I Ever Get Back to Oklahoma" Jason Boland
"Idabel Blues" Stoney LaRue
"Oklahoma Girl" Eli Young Band