Here are cities where I've lived at one time or another that had AT40 & CT40.
Charlotte, NC: It was on 1110 WBT (back when WBT had a Adult leaning Top 40 format), them moved over to their sister FM, WBCY, when it went Top 40 in the early 80's. AT40 stayed at WBCY until late 1989 when it was dropped due to a format change. WZZG (Z-95.1) then picked it up for about a year in 1990, until the station changed format to Oldies. Meanwhile, Dance-oriented CHR WCKZ (Kiss 102) picked up Casey's Top 40 when it started in 1989 and ran it until about 1992 when Kiss altered it's format toward Urban/Hip-Hop and dropped the show. CT40 reappeared in 1994 on WEDJ (The Edge 95.1) and kept the show when it became AT40 in 1998. By that time, the station had become WNKS (Kiss 95.1).
Columbia, SC: It was on WNOK as far back as I can remember listening to the show (1982) and kept the show until 1991 when it was dropped for CT40. CT40 was first heard on WYYS (Yes 97) in 1989, but dropped it in 1991 since Yes 97 had altered it's format to Rock 40 and no longer aired much of the music that was on the countdown. WNOK picked up the show about 2 weeks later and continues to air it on weekends.
Augusta, GA: WBBQ ran the show throughout the 1980's until it was dropped around 1991. They were running CT40 right from the start, so Casey Kasem was always heard on WBBQ. In 1994 WBBQ and AC WZNY swapped formats & airstaff and CT40 was moved to WZNY. They kept CT40 and AT40 until the station became Country WIBL (105.7 The Bull) in 2004. New CHR startup WHHD (HD98.3) now has AT40.
Charleston, SC: WTMA had the show in the 1970's and early 80's when it was moved to FM sister WSSX (95SX). 95SX kept the show until 1991 when it was dropped for CT40. About a year later, it was moved over to CHR LMA partner WSSP (Fly 94), which kept it for about a year, then the station changed format and dropped CT40. WSSX, by this time was AC and picked up CT20 for about a year and a half, then the station relaunched as a CHR in late 1995 and re-acquired AT40.
Greenville/Spartanburg, SC: WORD in Spartanburg and WQOK in Greenville both had it in the 70's. Back then, both cities were separate markets, but the consolidation of both cities into one single market eventually killed off both stations. WFBC-FM picked up AT40 in the early 80's until 1984 when they've changed over to AC, then WCKN (Rock 101) picked it up and ran it until 1987 when the format was changed to Album/Classic Rock. Then WANS ran AT40 until it was dropped in 1989 in favor of CT40. WANS flipped to AC in 1991 and dropped the show.
Robyn