Basically "IKEA" as a total entity is split into two parts, one is the stores and things related to that like customer support and property management. That bit is ultimately owned by a Dutch holding company and then a Dutch foundation.
The other bit is "the concept", the design and production of the furniture, and the logistics. That is ultimately owned by Interogo Foundation registered in Liechtenstein.
https://en.wikipedia.org/wiki/Template:IKEA_ownership_chart
In practice it's all controlled by the Kamprad family, which currently live in England and Belgium according to wikipedia.
Reportedly the reason to have ownership in the Netherlands is to avoid taxes, which is a integral piece of the IKEA culture of cheapness.
If the Netherlands would rewrite those laws, the Kamprads wouldn't be able to do what they're doing.