The incident was reported shortly before 1 p.m. at a home in the 2100 block of South Cedar Street, according to the Santa Ana Police Department.
Investigators determined that the toddler had entered the neighbor's yard by climbing over toys and other items that were stacked against a block wall at the back of his family residence.
Can you contract coronavirus in a swimming pool? Questions about COVID-19 answered by Pasadena doctor
After being found in the pool, the child was transported to Children's Hospital of Orange County where he was pronounced deceased, police said.
A chaplain was summoned to the hospital to assist the boy's grieving family.