Mainer may refer to:

• Mainer (American), a person from Maine
• Martin Mainer (born 1959), Czech artist and professor
• Wade Mainer (born 1907), American singer and banjoist

• USS Oneida (1898)
• USS Oneida (APA-221)
• Usson-en-Forez
• USS Oneota (AN-85)
• USS Oneota (YN-110)
• USS Oneyana
• USS Oneyana (YT-262)
• USS Oneyana (YTB-262)
• USS Oneyana (YTM-262)
• Us (song)
• USS Onkahye
• USS Onkahye (1843)
• USS Ono (SP-128)
• Usson, Puy-de-Dome
• Usson, Puy-de-Dôme
• USS Onset
• USS Onset (SP-1224)
• USS Ontario
• USS Ontario (1863)
• USS Ontario (AT-13)
• USS Ontario (ATO-13)
• USS Ontario (AT–13)
• USS Onward
• USS Onward II
• USS Onward II (SP-728)