From memory, there are exactly two scenes which take place outside the deliberation chamber, one at the beginning of the movie showing the last moments of the trial before the jury retires (and, crucially, it shows you the face of the defendemt). The other scene is at the very end, on the steps of the courthouse as the jurors depart. There's a brief instance of dialog between Fonda and the old man juror.

Still, hardly seems fair to hold these instances against calling the movie a one location picture.