The United States now enters the phase of mass executions.

[BrianSoddingBoru4]

This thread has drifted far from my original intent and purpose; but, here is one related definition:

Mass killing – Joan Esteban, Massimo Morelli, and Dominic Rohner define mass killings as "the killings of substantial numbers of human beings, when not in the course of military action against the military forces of an avowed enemy, under the conditions of the essential defenselessness and helplessness of the victims."[23] Valentino defines the term as "the intentional killing of a massive number of noncombatants",[24] where a "massive number" is at least 50,000 intentional deaths over the course of five years or less;[25] this is the most accepted quantitative minimum threshold for the term.[23][26]

50K deaths over 5 years would be amount to 28 deaths per day.

Wikipedia -- Mass killing

If you look in the bottom of the article, the 10 to 20K killed in Iran are classified as being a mass killing even though the killings occurred over the course of a decade.

I am not an expert, but, I will ask someone I know who is.

‘Mass killing’ and ‘mass executions’ are not the same thing. Based on your metric, the Dakota executions mentioned above stand as the ONLY mass execution in US history. Nine judicial killings over two months don’t even crack the top ten.

Boru