The leather accessory was a gift from his dad Eamon Farrell, a former soccer star who played for Ireland's Shamrock Rovers Football Club.
It is said to have been stolen a few weeks ago and the Minority Report star is desperate to get it back, according to Britain's The Sun.
A source tells the newspaper, "Colin has had this lucky leather belt for so long he just can't bear to get rid of it. The thing is literally coming apart at the seams.
"The belt has undergone numerous alterations, like having extra holes punched in it and extra leather added since he has gone through so many weight changes."
The Irish star and Polish actress Alicja Bachleda became parents to little Henry in October (09).
After jetting back to Farrell's native Ireland for the holidays, the couple was on hand to attend the star's brother Eamon's marriage celebrations in Dublin on Sunday (27Dec09). Eamon wed his longtime boyfriend in a same-sex ceremony in Canada over the summer (09), but organised a party in his hometown to celebrate the nuptials with his family and friends.
The couple then flew to Poland to visit Bachleda's family and organise a baptism for their son.
Farrell and Bachleda were photographed attending an hour-long service at a church in Krakow, Poland on Tuesday (29Dec09), according to Polish website Efakt.pl.
Farrell has another son, six-year-old James, with his ex-girlfriend Kim Bordenave.