The only way to reach Ilha Grande is by boat. Three mainland ports run regular services to Vila do Abraão.
From Angra dos Reis: The classic departure. State-run ferries (Barcas SA) take about 90 minutes and run twice a day; private fast catamarans take 30–40 minutes and run hourly. The ferry terminal is a 15-minute walk from the Angra dos Reis bus station.
From Conceição de Jacareí: A small fishing village halfway between Angra and Paraty on the BR-101. Schooner-style boats run several times a day to Abraão, taking about 50 minutes. Most direct transfers from Rio go via here.
From Mangaratiba: A daily ferry takes about 90 minutes. Slightly less convenient unless you are coming from the Rio side.
Getting to the ports: From Rio de Janeiro, regular Costa Verde buses run to Angra dos Reis (about 3 hours) and Mangaratiba; many tour operators run direct van services from Rio to Conceição de Jacareí.