Forty rallies will be held across the U.S., including ones in Kokomo and Fort Wayne.
A group of supporters met over the weekend to plan a separate "traditional prom" for Sullivan High School students that would prohibit gays from attending.
A Ball State survey shows 54 percent oppose a constitutional amendment banning gay marriage, while 38 percent support the proposed amendment.
The Indiana legislature will likely vote again next session on a constitutional amendment banning same-sex marriage.