Park said all her officials would cooperate actively with the police investigation.
The affair cast a cloud over Park’s US tour – her first overseas trip since taking office in February.
Park held a summit with President Barack Obama, at which the two leaders reaffirmed their united front of offering no concessions in the face of provocations from North Korea.
She also addressed a joint session of the US Congress, stressing that Pyongyang had to give up its nuclear weapons.
North Korea was quick to pick up on the Yoon scandal, with the ruling party newspaper Rodong Sinmun crowing in a commentary Sunday that Park’s US trip would be remembered for a “shameful” act of indecency.