We could not find this information specifically for people living with dementia. However, it has been estimated that around 100,000 people live in such facilities, of which 84,000 are older people, and the remaining are younger people with mental illness or disabilities (Camarano & Kanso, 2010).

References:

Camarano, A. A. & Kanso, S. (2010). As instituições de longa permanência para idosos no Brasil. Revista Brasileira de Estudos de População, 27(1), 232–235. https://doi.org/10.1590/S0102-30982010000100014