Apparently, you're not going to accept Kent State, but there are non-National Guard incidents from earlier than that. The Bonus Army protesters in 1932 were cleared from DC by the tanks of the 3rd Cavalry commanded by no less than George Patton. Unfortunately, there is no record of total deaths. 5 infantry regiments fresh out of Gettysburg were sent to quell the New York City draft riots in 1863. Again, not known how many they killed, but total deaths well into the hundreds.
This is to say nothing of the many, many times the Army was used to clear natives from lands claimed by the US. Presumably, in most of those incidents, they were not considered American citizens. However, they definitely were in the most recent incident I can think of, the Wounded Knee massacre, which happened in 1980. That was the 7th Cavalry, and they killed 250 Lakota, including women and children.
This is to say nothing of the many, many times the Army was used to clear natives from lands claimed by the US. Presumably, in most of those incidents, they were not considered American citizens. However, they definitely were in the most recent incident I can think of, the Wounded Knee massacre, which happened in 1980. That was the 7th Cavalry, and they killed 250 Lakota, including women and children.