Ken Ilsø

Born in Copenhagen, Ilsø started his footballing career at local amateur club BK Pioneren. He subsequently was joined by his brother Marco Ilsø, playing for several youth teams in Copenhagen. In 2004, he was signed as a youth player by Dutch side SC Heerenveen, after being labelled as one of Denmark's finest talents. On 16 April 2006, he made his senior team debut for SC Heerenveen, also his only senior appearance with the club, in an Eredivisie match against AZ Alkmaar as a 75th-minute substitute for teammate Arnold Bruggink.

SC Heerenveen

Following his first-team debut with SC Heerenveen, Ilsø never managed to make another senior team appearance for the rest of his time at the club. He had a brief loan spell with FC Zwolle on-loan from SC Heerenveen, but did not make a single appearance for the Dutch club.

SønderjyskE

Unable to break into the first-team plans of SC Heerenveen, Ilsø returned in 2007 to Denmark, and joined local club SønderjyskE. He had a more successful spell with SønderjyskE, scoring 12 goals in 52 league matches for a side that was threatened by relegation.

FC Midtjylland

In summer 2009, Ilsø was signed by FC Midtjylland, who ended in the fourth spot of the Superliga the prior season. Ilsø quickly became an important player for FC Midtjylland. For instance, in the 2010–11 season opener against Silkeborg IF, Ilsø scored the decisive goal to earn a win for the club .

Fortuna Düsseldorf

Following his performance with FC Midtjylland, Ilsø joined 2. Bundesliga club Fortuna Düsseldorf on-loan in the 2010 winter transfer window. Fortuna Düsseldorf subsequently signed him permanently in the following year's summer transfer window, for a reported fee of €300,000. By the end of the 2nd Bundesliga 2011–12 season, Fortuna Düsseldorf was in the 3rd place, and had to face Hertha BSC in the promotion/relegation play-off. Across both legs of the play-off, Ilsø assisted twice, once in each leg and therefore helped Fortuna to promote to the Bundesliga as the…

Midtjylland

Danish Cup runner-up: 2010 Home United

Singapore Cup runner-up: 2015 Kedah

Malaysian Charity Cup: 2017 FA Cup: 2017 Adelaide United

FFA Cup: 2018