Family
- mother Rita Farrell:
- sister Catherine Farrell:
- son James Farrell: Born Sep. 12, 2003; mother Kim Bordenave; diagnosed with Angelman syndrome, a rare neurogenetic disorder that slows development and impairs speech and motor skills
- father Eamonn Farrell: Played Irish football for the Shamrock Rovers
- uncle Tommy Farrell: Played Irish football with the Shamrock Rovers
- sister Claudine Farrell: Works as Colin's assistant
- brother Eamonn:
Companions
- Britney Spears : alleged brief romance, early 2003
- Kim Bordenave : alleged affair in early 2003; reportedly carrying Farrell's child, early 2003
- Companion Alicja Bachleda: Reportedly dating as of Spring 2009
- Companion Lake Bell: Met on the set of "Pride And Glory" (2008); rumored to have briefly dated in 2006
- Companion Emma Forrest: Split in February 2009 after dating for several months
- Companion Kim Bordenave: Began dating c. 2002; split shortly after the birth of his son James (September 2003)
- Companion Muireann McDonnell: Irish medical student; began dating summer 2007
