The 27-year-old, a former England Under-21 goalkeeper, was a marquee signing by the Millers last summer, but failed to show his pedigree.
He made just four appearances for Steve Evans' men and did not feature for them after a poor display against Ipswich in September, spending time on loan at Bury, Peterborough and Yeovil before the season was out.
Evans told him he was free to find another club when he announced the club's retained list in early May and he has today hooked up with fellow ex-Miller Rob Milsom at Notts County, penning a two-year deal at Meadow Lane.
Loach's exit comes on the same day as as Rotherham announced the signing of Derby goalkeeper Kelle Roos on a season-long loan.
A club statement read: "The club would like to thank Scott for his effort and professionalism during his time with the club, and wish him the very best for the future."
