Do you need a green card to go college if have an American high school diploma?

No, having an American high school diploma does not automatically qualify you for a green card. A green card is required for permanent residency in the United States. While you may be eligible to attend college in the US with an American high school diploma, your immigration status (whether you're a citizen, permanent resident, or on a visa) will determine your eligibility for things like financial aid and the ability to legally work in the US while studying. You may need a student visa (F-1) if you are not a US citizen or permanent resident.