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Chikungunya virus (CHIKV), a mosquito-borne alphavirus, has traditionally circulated in Africa and Asia, causing human febrile illness accompanied by severe, chronic joint pain. The Asian and East-Central-South African (ECSA) genotypes were introduced in Brazil in 2014, in Bahia State and Northeast region. CHIKV virus rapidly spread, causing epidemics in urban areas, and the ECSA genotype was detected also in other regions. In the last five years, more than 700,000 cases of Chikungunya fever were reported in Brazil. Nevertheless, there is limited information about the genomic epidemiology of CHIKV from surveillance studies. In São Paulo (SP), the most populous Brazilian state, until 2015 only imported cases were identified. In 2020–21, an outbreak was detected in the coastal region of SP, accounting for 98% of confirmations in SP. To better understand the disease dynamics in SP, we generated 53 nearcomplete genomes of CHIKV isolates from Baixada Santista, obtained from clinical samples. Our results demonstrate that SP-CHIKV clade belongs to a distinct clade from those previously found in Brazil, supporting the local circulation of a specific lineage in the period. None of the SP-CHIKV carry the substitutions A226V (E1 protein) and L210Q (E2 protein) associated with increased transmission in Aedes albopictus mosquitoes. The results confirm that the ECSA lineage continues to spread across the country and reinforce that genomic data can provide information about virus genetic diversity and transmission dynamics, assisting the establishment of a more effective surveillance framework.