Flagler, 47, had been a firefighter for 21 years - first serving 19 years with the city of Vernon and then moving to the county agency in October 2020.
He is survived by his wife Jenny and two sons, ages 15 and 13.
During a press conference, officials said the fallen firefighter was pulled out from inside the burning home.
LA County firefighter dies after being pulled from burning house in Rancho Palos Verdes
The vigil was one of several tributes for Flagler.
On Saturday, firefighters stood on top of their engines overlooking the 5 Freeway in his honor.
The firefighters' union has established a memorial fund to benefit the family.