The sacroiliac joints reside concerning the sacrum (the tailbone segment of your spinal column) as well as the well known wing-like iliac bones that form the pelvic girdle. There are two SI joints, 1 on the still left and 1 on the right (highlighted in crimson in the graphic earlier https://www.theorthopaedicandpainpractice.com/service/hip-groin-pain/