Having made Steve Evans their new manager towards the end of last season and then made a host of signings this summer, the Millers are the clear favourites to lift the League Two title next May.
Exiled at Sheffield's Don Valley Stadium after leaving their old Millmoor home, over 6,000 fans turned out to see Rotherham defeat Barnsley 2-1 at the weekend.
Northampton host the Millers in their first home league game of the season on 21 August before travelling to the New York stadium at the start of February.