Where to continue the Hajime no Ippo manga

Hajime no Ippo by George Morikawa, 1989. The manga is still ongoing.

• Season 1 (75 episodes): Continue the manga from chapter 270 in volume 31.
• Champion Road: Continue the manga from chapter 315 in volume 35. This TV special covers Ippo's first title defense against Sanada, but jumps past the Kimura vs Mashiba title fight in chapters 270 to 290. Read that first if you came straight from Season 1.
• New Challenger (26 episodes): Continue the manga from chapter 421 in volume 47. This season skips the flashback to Kamogawa's youth in chapters 399 to 414. Rising adapts it at the very end, so read those first if you stop here.
• Rising (25 episodes): Continue the manga from chapter 559 in volume 61. The final four episodes are a flashback to Kamogawa's youth. The main story left off at chapter 558, so that is where you continue.