Location of a battle that killed nearly 300 Native Americans and about 25 American soldiers

I think that you are talking about Wounded Knee Massacre, as known as the Battle of Wounded Knee. These events took place on 1890, on the Lakota Pine Ridge Indian Reservation, South Dakota State. On December 15th, the trigger was the arrest of Sitting Bull, a Sioux chief who was practicing a dance. He was killed in the process. But on December 29th, another dance became into a fight between indians and american soldiers and this time, a massacre fallowed to a shot (which is not clear the side), and the events develop into more than 200 indians dead - mostly kids and women - and 25 men from US Army.