Answer: What you are asking for is very difficult. If by "ground cover" you were referring to some of the traditional covers such as ivy, euonymus, vinca or Ajuga, covering such a large area would be very difficult if not impossible by seeding it. Perhaps a better answer would be to allow the grass to grow. It's ultimate growth would probably be only about 6" to 12" depending on the variety that you have. Mown once or twice a season, it could do quite nicely once you adjust to the new look of the grass.
Another option would be to kill all the grass, and plant a "wildflower meadow." This can be done by seeding, although to be successful, it will be necessary to be able to keep the young plants watered till they are established. Most wildflower seedings contain mostly annual flowers, which means that next year you will again have to decide what to do.
A more permanent area could be established with native prairie plants, and while this can be established with seeds, a better option is using plants to deter the many weeds that will inevitably work their way into your "prairie" while it is becoming establish. Most areas such as this are a surprising 4' to 8' tall when established. For more information on establishing a wildflower or native plant area, contact the Indiana Native Plant and Wildflower Society at http://www.inpaws.org/
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