Brierley's barrister admitted he possessed "some images" but the exact figure is "in dispute".
The New Zealand businessman was arrested in December 2019 on six counts of possession of child abuse material.
Border officials had found child sexual abuse material on his laptop and electronic storage devices.
Brierley will be sentenced on 30 April.
This evening Cricket Wellington, where Brierley was a former Patron and current life member, said it was "shocked" to learn of his guilty plea.
"Following this morning's guilty plea this status will now be reviewed," it said in a statement to 1 NEWS.
Cricket Wellington has not received donations from Brierley since October 2017.