All are true about iliolumbar ligament, except
Ref. Gray’s anatomy.  41st edition. Page. 1090
 
Ilio-Lumbar Ligament:
The portion of the iliolumbar ligament originating from the L-5 transverse process is made up of two bands (anterior and posterior).
The anterior band is broad and flat and has two different anatomic varieties. 

Type 1 originates from the anterior aspect of the inferolateral portion of the L-5 transverse process and fans out widely before inserting on the anterior portion of the iliac tuberosity.
Type 2 originates anteriorly, laterally, and posteriorly from inferolateral aspect of the L-5 transverse process and fans out before inserting on the anterior portion of the iliac tuberosity.

 It is probable that the spatial disposition of the iliolumbar ligament influences its antitorsional role
Origin: transverse process of L5
insertion: deep into ventral margin of iliac crest 6-7cm from midline
The main part of ILL originates from L5 transverse processes. insert was shield by crest dorsally,making it inaccessable to palpation.
Attached to transverse process of L4
Lower part attached to sacrospinous ligament
It is attached to iliac crest
Superiorly continuous with thoracolumbar fascia