Thousands were expected at the protest near Seoul's City Hall, and more than 10,000 officers were being deployed amid concerns of clashes.
People in the crowd held up Korean and some US flags as well as portraits of the former leader.
Opponents and supporters of Park have filled the capital's streets with passionate rallies in recent months, reflecting the country's deep divide.
Park was jailed yesterday over allegations that she colluded with a confidante to extort money from businesses, take bribes and allow the friend to unlawfully interfere with state affairs.
Prosecutors can detain Park for up to 20 days, during which they are expected to formally charge her. A conviction for bribery alone would carry punishment of 10 years to life in prison.
She has denied most of the allegations against her. She has said she let her friend edit speeches and assist her with unspecified public relations duties.
Disclaimer: No Business Standard Journalist was involved in creation of this content
