This morning Tim Synowiec, a high school senior from Salisbury, MD who has a 9:16 3200 pb, took home the title at the 2022 Salisbury Marathon. He did so in style, clocking 2:22:51, breaking the 49-year old HS record on a records-eligible course of 2:23:47 set by Mitch Kingery way back in 1973. Kingery, who ran 4 marathons in a six week period, set his mark as a sophomore in high school at age 16.
The fastest marathon run by a US high schooler today was 2:23:05 run by Clance Devery in 1977 but that was an aided net downhill course.
Here is some more info on the HS marathon record.