County went in front at the New York Stadium on Saturday through Yoann Arquin but Rotherham levelled before half-time courtesy of Ben Pringle and neither side could find the winner after the break.
The visitors struck first blood after 32 minutes with a quality strike.
Arquin met Alan Sheehan's cross from the left and struck a sweet volley on the angle from 20 yards to claim his seventh of the season.
Three minutes before the break Rotherham levelled after their best period of the half.
Daniel Nardiello's determination paid off when he sent Michael O'Connor down the left and his inviting low cross was met by Pringle on the run to drill a shot out of Bartosz Bialkowski's reach in the County goal.
The Millers could had grabbed the lead but Mark Bradley hit the post and Alex Revell steered a header over before half time.
Hamza Bencherif went close from a Sheehan corner in the second period but his header was wide.