Suits were filed on behalf of Tammy VanDam of Wanatah, Indiana, 42, the mother of a 17-year-old daughter, and her partner Beth Urschel, 49.
VanDam was killed by the collapse of the stage after a high blast of wind whipped through the grandstand area just minutes before the country duo Sugarland was scheduled to perform. Urschel was severely injured.
Although Indiana law does not recognize the rights of same-sex couples, "this is an inequity we also intend to address in this lawsuit," Kenneth J. Allen, an attorney for the plaintiffs, said in a statement.
"Tammy's death is not only devastating for Beth, it also leaves her daughter without a mother's love and guidance during the most vulnerable stage of her life," Allen said.
Allen said Beth Urschel suffered "serious and painful crush injuries" and will have lifelong impairment. Defendants include Mid-America Sound Corp, Live Nation Worldwide and Lucas Entertainment Group.
Indiana Governor Mitch Daniels has asked the Indiana Inspector General to assign several staffers to the State Fair Commission to assist in the fact finding and documentation procurement aspect of an investigation into the incident.
The fair commission has hired Thornton Tomasetti, a New York engineering company, to coordinate and conduct the structural portion of the investigation.
The Washington D.C.-based firm of Witt Associates will do an analysis of the fair's preparedness and response to the event.
"This was a terrible tragedy that could and should have been prevented; the responsible parties must be held to account," Allen said.