Nilópolis (Portuguese pronunciation: [niˈlɔpoliʃ], [niˈlɔpɔliʃ], [niˈlɔpuliʃ]) is a municipality in Brazil, located in the Rio de Janeiro state's southwestern region, bordering São João de Meriti, Mesquita and Rio de Janeiro.

It is the smallest municipality in Rio de Janeiro state, with a total area of 19.39 km2.

Currently, São João de Meriti has the highest population density, with 12,897 inhabitants/km2.

The city was named after Nilo Peçanha, a President of Brazil.

Nilópolis is famous for its Grêmio Recreativo Escola de Samba Beija-Flor de Nilópolis, one of the most successful and luxurious Samba schools and usually a top contender for winning the carnival parade in Rio.