Depends on what you consider a "shooting". Typically, the media is referring to the Bath School Disaster of 1927, in which 44 people died, including 38 schoolchildren. Most of the deaths in that attack were caused by bombs, but several people were shot to death as well.
If the meaning of "shooting" is expanded to domestic rebellions, insurrections, and outright battles, then any of the recent mass shooting is far from the top of that list. A few "not modern" examples:
The Stono Rebellion occurred on September 9, 1739, in the colony of South Carolina. It was a slave rebellion in which approximately 75 people were killed. (Source.)
The Nat Turner Rebellion occurred from August 21-23, 1831, in Southampton County, Virginia. There were approximately 175 black slaves and white militiamen killed in the rebellion itself, with an additional 56 slaves executed after the rebellion was put down. (Source.)
The New York Draft Riots occurred during the Civil War, from July 13-16, 1863, in Manhattan, New York City. About 120 people were killed in the riots. (Source.)
The Wilmington Insurrection of November 10, 1898, saw a mob of 2000 white men overthrow the democratically elected government of Wilmington, North Carolina, upset that the city council just elected for the next term was to be 1/3 black. As many as 60 black residents of Wilmington were killed in the riot. (Sources 1, 2.)
The Battle of Blair Mountain occurred between August 25 and September 2, 1921, in Logan County, West Virginia. It was the biggest labor uprising in U.S. history, and a legitimate battle. 10,000 coal miners organized and confronted a force of 3000 strikebreakers and law enforcement officers and the battle resulted in as many as 110 deaths. (Source.)
So the media's language about "modern" history is, first of all, to distinguish it from the Bath School Disaster, in case the raw numbers being reported do not exceed that disaster. But secondly, it's to distinguish the mass shootings from earlier armed incidents of civil unrest, including labor uprisings, slave uprisings, and white supremacist uprisings, and other uprisings that occurred before World War II.