Simran, who had won the bronze in the 40 kg category at the 2017 Cadet World Championships, lost 6 to 11 while the US posted a point victory to win the gold medal on Saturday night.
Simran conceded a 2 to 9 lead over Shilson in the first period, virtually sealing his fate.
The Indian produced a better performance in the second period by scoring four points against two for his American opponent, but this turned out too little, too late to have an impact on the outcome of the match.
Shilson is the 43 kg gold medalist at the 2018 Cadet World Championships.
It is India's fifth silver medal with three gold medals in the ongoing Youth Olympic Games. Medals won by Lakshya Sen (gold), shooter Manu Bhaker (silver) and judoka Tababi Devi (silver) in the mixed team events do not count towards the country's total medals because they were associated with athletes from other countries.
The other Indian in the wrestling competition, Mansi, finished eighth after losing her ranking match against Imbabi Ahmed of Egypt, who received a decision of "victory by fall" .