Onstad is a Norwegian surname. Notable people with the surname include:
Chris Onstad, American writer, cartoonist, and artist
Erik Gjems-Onstad, Norwegian resistance member, lawyer, and politician
Kari Onstad, Norwegian singer and actress
Katrina Onstad, Canadian critically acclaimed journalist and novelist
Kenton Onstad, American politician, member of the North Dakota House of Representatives
Kristian Flittie Onstad, Norwegian professional footballer defender
Niels Onstad (1909-1978), Norwegian shipping executive
Ole Gjems-Onstad, Norwegian jurist
Otto Onstad (1874-1961), American politician
Pat Onstad, Canadian professional soccer goalkeeper