His body was found on Bukak mountain in the Seongbuk-gu neighborhood, which is close to his official residence in Jongno-gu.
Police said that his body was found at Mt Bugak in northern Seoul around midnight, near where his phone signal had last been detected.
Park, 64, had reportedly faced a probe into allegations of sexual harassment against a former female secretary.
The short note, seen as his will unveiled by the city government, said, "I'm sorry to everyone".
The mayor of a city of 10 million residents, Park was one of the most powerful elected officials in the country and was widely considered a potential presidential candidate for the ruling Democratic Party in 2022. A memorial altar will be set up in front of the City Hall in central Seoul Friday afternoon to allow citizens to mourn his death.
Meanwhile, there was an unidentified article on the Internet claiming to reveal the contents of the sexual harassment complaint.
Lockdown in major state as India COVID-19 cases soar
It took 110 days for the number of cases in the country to reach one lakh but just 53 days more to race past the eight-lakh mark. The city, however, has strengthened its recovery rate to more than 77%, which means that 3 out every 4 patients have recovered.
Samsung may skip in-box phone chargers from early next year
South Korean tech giant Samsung is reportedly considering selling smartphones without in-box chargers from as early as next year. Considering if this does happen next year, Samsung phone prices may come down but by how much, can not be said at this point.
Vettel is bound to be distracted by Ferrari axe, says Brawn
Sebastian Vettel expects his on-track battles with Charles Leclerc to continue in the 2020 season even though he is leaving Ferrari .
Rep. Yoo Sang-bum of the United Future Party said in a radio interview that "I felt deeply sorry for the deceased, but I think there's a need to sufficiently examine what happened in the runup (to his death)".
Park was first elected mayor of Seoul in October 2011 as an independent, although he was strongly supported by the Democratic Party, which presently has a large majority in the national parliament, and the left-of-center Democratic Labor Party.
His daughter had filed a missing complaint at 5.17 p.m. KST on July 9. The Prime Minister, Chung Sye-Kyun, expressed his condolences during a regular government meeting in response to the global pandemic.
Choi Ik-su, an official from the Seoul Metropolitan Police Agency, said salvage hounds discovered Park's body, and that his sack, cellphone, and business cards had been recuperated.
Kim Chong-in, caretaker leader of the conservative main opposition United Future Party, had put a plan on hold to pay a condolence call to Park's family.
Mr Park also praised women for their courage after a series of women accused powerful politicians and policymakers of sexual wrongdoings amid the #MeToo movement in 2018. He was a human rights lawyer and had founded an influential civil rights group before his election.
As mayor, Park championed city welfare projects and became a symbol of reform.