Eastham is available on a free transfer after seeing out his contract at Bloomfield Road earlier this summer.
Blackpool were keen to keep the 22-year-old, but Eastham decided to move in search of regular first-team football.
The highy-rated centre-back spent most of last season on loan at Bury, as well as spells at Fleetwood and Notts County, to continue his development.
A number of clubs expressed an interest in signing Eastham, but Rochdale have won the race for the player's signature.
Eastham has agreed a two-year deal with Keith Hill's side as he looks to build a squad capable of winning promotion to League One.