Tonantins is a municipality in the state of Amazonas in north-western Brazil. Its population was 18,897 as of 2020, all of which were Brazilians. It is on the Amazon River and is 867 km upstream (west) of Manaus, the state capital. The municipality is directly east of and overlaps parts of the Jutaí-Solimões Ecological Station. It is only accessible via boat.