Onezhsky (masculine), Onezhskaya (feminine), or Onezhskoye (neuter) may refer to:

• Onezhsky District, a district of Arkhangelsk Oblast, Russia
• Onezhskoye Urban Settlement, a municipal formation within Onezhsky Municipal District which the town of oblast significance of Onega in Arkhangelsk Oblast, Russia is incorporated as
• Onezhsky (rural locality), a rural locality (a settlement) in the Republic of Karelia, Russia
• Onega Peninsula (Onezhsky poluostrov), a peninsula in Arkhangelsk Oblast, Russia
• Lake Onega (Onezhskoye ozero), a lake in the northwest of Russia
• Onega Bay (Onezhsky zaliv or Onezhskaya guba), a bay in the northwest of Russia