The 20-year-old Denmark international feels Villa were the team for him, and a talk with boss Paul Lambert was a decisive factor in his decision.
"I have a good feeling it was the right decision to turn down Chelsea," Okore told Sporten.dk.
"I feel that I have arrived at a club that believes in me.
"The manager has said all the right things and that has caught my attention. This is going to be good."