Arlo's single hit #18 in 1972 -- the only pop hit version.
As a minor addendum: Steve Goodman's own rendition of the song "bubbled under" at #113 in January 1972, according to
The Buddah Box.
Sales info is trickier to come by: with a Billboard subscription, you can get access to that kind of data, but I don't know how to do so for free. And I don't own any album chart encycs -- but I can tell you that the following JD singles are certified gold, reflecting sales of at least 500,000 copies:
Take Me Home, Country Roads
Sunshine On My Shoulders
Annie's Song
Back Home Again (nb: I have never heard this song)
Thank God I'm a Country Boy
I'm Sorry / Calypso (double-sided single, but only side A is certified gold; I don't know how this works; further, I've never heard either side of this either.)
P.S. I don't care how uncool he was, his Christmas disc with the Muppets is my favorite holiday record of all.