Rhodes, who now has 21 goals for club and country this season, headed the opener 26 seconds into the second half from Jack Hunt's curling cross then struck a stunning breakaway goal after Town had had Alan Lee sent off.
Lee, who had running feud with County's Sam Sodje, was shown a straight red card for retaliating with his elbow after being fouled by Sodje in the 61st minute.
The visitors chased an equaliser, but got caught when Rhodes romped away down the middle in the 65th minute and hit a powerful low drive past goalkeeper Stuart Nelson.
County had half-chances, but rarely tested Town goalkeeper Ian Bennett. They got a consolation though in the fourth minute of stoppage time when Neal Bishop's 18-yard drive was deflected in.
The Terriers have broken Nottingham Forest's 33-year-old unbeaten league record set under Brian Clough. Town's last league defeat was against Southampton in December last year.
