If confirmed, it would be the largest protest in Hong Kong's history. Police said turnout was 338,000 at its peak.
The masses turned out despite the suspension of the bill - which would allow extradition from Hong Kong to mainland China - on Saturday.
Hong Kong leader Carrie Lam on Sunday apologised for proposing the bill.
Many protesters, who fear increased Chinese influence over Hong Kong, are calling on her to resign over the unrest.
They are also demanding that the bill be scrapped, not just suspended.