The 24-year-old Bantams striker has penned a two-year deal, leaving Valley Parade for an undisclosed fee.
Poleon, who has also played for Leeds United and Sheffield United on loan, made 37 appearances for the Bantams last season following his switch from AFC Wimbledon in June 2017, netting seven times.
Tom Bradshaw remains a Barnsley player after the club rejected two bids from Championship rivals, one of whom is Millwall.
The Wales international, last season’s top-scorer for the Reds, has been the subject of considerable interest from the second tier, with Rotherham United, Bolton Wanderers and Reading also in the running.
Sheffield Wednesday defender Jack Hunt is set to be confirmed as a Bristol City player later today after undergoing a medical on Wednesday night after a £1.6m move.
Hunt, who has made 96 appearances for the Owls, is set to become Lee Johnson’s fifth signing of the summer, after the Robins sealed deals for Ipswich defender Adam Webster, Derby forward Andreas Weimann, Norwich winger Marley Watkins and Scunthorpe winger Hakeeb Adelakun.
The Owls have reportedly made an enquiry regarding Peterborough United defender Jack Baldwin.
Sheffield United’s quest to sign big striking target Sam Gallagher could move a step closer if Southampton are successful in their pursuit of Liverpool forward Danny Ings, who is set to leave Anfield this summer.
Officials at Bramall Lane and St Mary’s are understood to have discussed Gallagher’s situation again this week, with the Blades’ transfer kitty fortified by proceeds from the big-money sale of midfielder David Brooks to Bournemouth.
Hull City have shown an interest in signing PSV Eindhoven defender Jordy de Wijs, according to reports in the Netherlands.
The 23-year-old impressed during a loan spell at Eredivisie outfit Excelsior last season and has made a number of appearances for the Netherlands’ international youth sides.
Italian club Perugia also also showing an interest, but the defender is said to favour a move to the Championship.
Middlesbrough defender Fabio da Silva has been the subject of a failed £300,000 bid from Nottingham Forest, managed by former Boro chief Aitor Karanka.