The 29-year-old, who played for Rotherham between 2006 and 2010, has been without a club since leaving Macclesfield Town at the end of last season.
However, Rotherham boss Steve Evans, who managed the centre-back at Crawley, has handed the experienced defender the opportunity to secure a contract this summer.
Mills played for Rotherham reserves in a 3-0 win over Hartlepool United on Monday.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Wycombe WanderersWycombe | 14 | 10 | 2 | 2 | 32 | 16 | 16 | 32 |
| 2 | Birmingham CityBirmingham | 13 | 9 | 3 | 1 | 24 | 12 | 12 | 30 |
| 3 | Wrexham | 14 | 8 | 4 | 2 | 22 | 10 | 12 | 28 |
| 4 | Barnsley | 14 | 7 | 4 | 3 | 23 | 18 | 5 | 25 |
| 5 | Lincoln CityLincoln | 14 | 7 | 4 | 3 | 21 | 17 | 4 | 25 |
| 6 | Stockport CountyStockport | 15 | 6 | 6 | 3 | 25 | 17 | 8 | 24 |
| 7 | Mansfield TownMansfield | 13 | 7 | 3 | 3 | 20 | 15 | 5 | 24 |
| 8 | Huddersfield TownHuddersfield | 14 | 7 | 2 | 5 | 21 | 14 | 7 | 23 |
| 9 | Reading | 14 | 7 | 2 | 5 | 22 | 21 | 1 | 23 |
| 10 | Bolton WanderersBolton | 14 | 7 | 2 | 5 | 22 | 24 | -2 | 23 |
| 11 | Exeter CityExeter | 13 | 7 | 1 | 5 | 14 | 10 | 4 | 22 |
| 12 | Peterborough UnitedPeterborough | 15 | 6 | 3 | 6 | 31 | 27 | 4 | 21 |
| 13 | Charlton AthleticCharlton | 14 | 5 | 4 | 5 | 15 | 15 | 0 | 19 |
| 14 | Stevenage | 15 | 5 | 3 | 7 | 11 | 16 | -5 | 18 |
| 15 | Rotherham UnitedRotherham | 15 | 4 | 5 | 6 | 14 | 18 | -4 | 17 |
| 16 | Bristol Rovers | 14 | 5 | 2 | 7 | 16 | 21 | -5 | 17 |
| 17 | Northampton TownNorthampton | 14 | 4 | 4 | 6 | 18 | 21 | -3 | 16 |
| 18 | Blackpool | 14 | 4 | 4 | 6 | 21 | 28 | -7 | 16 |
| 19 | Wigan AthleticWigan | 14 | 3 | 5 | 6 | 12 | 12 | 0 | 14 |
| 20 | Leyton Orient | 14 | 4 | 2 | 8 | 14 | 18 | -4 | 14 |
| 21 | Crawley TownCrawley | 15 | 3 | 3 | 9 | 14 | 27 | -13 | 12 |
| 22 | Cambridge UnitedCambridge | 13 | 3 | 1 | 9 | 12 | 23 | -11 | 10 |
| 23 | Burton Albion | 14 | 1 | 5 | 8 | 15 | 25 | -10 | 8 |
| 24 | Shrewsbury TownShrewsbury | 15 | 2 | 2 | 11 | 13 | 27 | -14 | 8 |
| > League One Full Table | |||||||||
