The former Cat and Bulldog, 28, has agreed to a one-year deal with the Joeys after deciding against an interstate move to SANFL club North Adelaide.
Street played 17 games for Geelong between 2001 and 2003 and 61 for the Dogs from 2004 and 2008.
The big man said "staying local" was the main reason behind his decision to reject the chance to play in South Australia and take on the assistant coaching/ruckman role with the Joeys.
"It was one of the really hard decisions and probably the toughest couple of weeks I've experienced," Street told the Geelong Advertiser on Wednesday.
"I had a lot of clubs come to me and they were all fantastic, and it just made it so much harder to make a decision.
"A lot of people have asked me why I didn't play VFL, but I've played a lot of VFL footy and if it can't be AFL, then right now I think this is where I'd prefer to be; close to home.
"I had a good offer from South Australia to play for North Adelaide, seven GFL clubs rang me and a couple from as far away as Swan Hill and Shepparton all offered coaching positions, but I wasn't really interested.
"I wanted to stay local. My wife's a Geelong girl, her family all live here and we've got a young boy, so everything is all set up in Geelong and it would had to have been a pretty good offer for me to move elsewhere."
St Joseph's president Mark Jackman said the club was excited about Street's crowd-pulling potential and described the signing as "fantastic".
He also said the club would not stand in Street's way if he was drafted by an AFL club during the November 29 draft. The Brisbane Lions may be interested in the 211cm ruckman, after the retirement of Beau McDonald and the delisting of rookie Joel Tippett.