Cooney gave away the news on Friday when he changed his Twitter account handle to @Adamcooney13.
He wore the No. 17 guernsey in his 219 games with the Western Bulldogs.
Long wore both No. 4 and No. 13 in his 190 matches for the Bombers, winning both of his premiership medals in the No. 13.
Young star Zach Merrett will also wear a new number in 2015, taking on the No. 7 guernsey vacated by Leroy Jetta.
Merrett wore No. 27 in his debut season, which saw him nominated for the NAB AFL Rising Star.
Essendon will announce other number changes when it finalises its list after the NAB AFL national and rookie drafts.
Long's son Jake is a chance to be added to the Bombers' rookie list on December 3.
