Green’s Dictionary of Slang

a fool, a yokel.

c.1534		P. Vergil Eng. Hist. (translation) (1846) I 285: Fallinge into [...] altercation with a stronge stubberne clomperton, he was shrowdlie beaten of him [N].
1822		R. Nares Gloss. (1888) I 167: †clomperton. A clown.
1870		All the Year Round 5 Mar. ‘Byegone Cant (Geo. II) n.p.: Clumpertons agape at the giant proportions of the still somewhat new St. Paul’s would turn from their wondering walks to shudder and shrink at the ghastly gallows exhibition at Newgate [F&H].
1877		Sussex Advertiser 23 June 4/6: That bag had something in it worth nailing [...] but you, you cursed ninny, coolly handed it back to the clumperton.