Oncken is a surname. Notable people with the surname include:
Arthur Oncken Lovejoy, a German-born American philosopher
August Oncken (1844–1911), a German economist (German article)
Hermann Oncken (1867–1945), a German historian
Johann Gerhard Oncken (1800–1884), a pioneer German Baptist preacher
Onno Oncken, a geologist
Wilhelm Oncken (1835–1905), a German historian