The final notes of a surprise “Ohio” — the protest song about the shootings at Kent State — faded away, and Neil Young looked at Saturday’s full crowd of 24,000 at the Xfinity Theatre in Hartford, Conn. “Where are you going tomorrow?” Young shouted. “Farmer’s market!” people called back, primed by the folk-rock icon’s prior appeals to stop at a roadside market, starting the next day.

Neil Young (left) and John Mellencamp (right) at the at the 33rd annual Farm Aid concert

That simple way to help local farmers supplemented a message to stand against the corporatization of farming during the 33^rd annual Farm Aid concert, which hit Connecticut with an all-star cast also including fellow principals Willie Nelson, John Mellencamp and Dave Matthews. It was only the event’s second time in New England, following a stop Mansfield’s then-Comcast Center in 2008.

The 10-hour-plus show leaned to country music long before patriarch Nelson closed the marathon with “Will the Circle Be Unbroken” and “I’ll Fly Away,” boosted by singer/guitarist son Lukas and guests Margo Price and Nathaniel Rateliff, both honorary family members on their concurrent Outlaw Music Festival tour.

Sturgill Simpson (left) and Kacey Musgraves (right) at the 33rd annual Farm Aid concert

That country still came with rock backbone from Chris Stapleton (whose gritty, whisky-soaked hillbilly tunes were iced by Nelson’s harp player Mickey Raphael) and Outlaw tour participant Sturgill Simpson, whose classic country voice was outweighed by gnarly, amped-up jams with his quartet. Simpson kicked up more guitar sparks than anyone on the program short of Young, even covering the blues-rock standard “Going Down.” By contrast, Jamey Johnson took the stripped-down route, standing alone on the big stage to clutch his legend-autographed acoustic guitar and intone hardscrabble tales with sobering focus in songs like “High Cost of Living” and “The Dollar.”

Kacey Musgraves struck a more precious pose with her glamorous pop-country (down to the club-style beat in her “High Horse”), but her backing band was just as polished and her voice a clarion flutter in “Butterflies.” Margo Price stuck closer to the Americana side of country, from apt opener “All American Made” (playing piano before moving to guitar) to closer “Cocaine Cowboys,” where the singer hopped aboard a second drum kit. Price also synced up with farmers’ plight, noting her own family lost their farm to foreclosure. The only exception to the show’s country midsection came from Rateliff, who put some zip into the afternoon with his Night Sweats’ hearty, horn-iced R&B-soul, capped by a cover of the Band’s “The Shape I’m In” with cameos by Price and Lukas Nelson.

Rising star Lukas Nelson proved the day’s most valuable player between cameos and rousing sets with his band the Promise of the Real, which played on its own early in the afternoon and then backed Young that night. Nelson ripped a mean guitar, sang with a resonant timbre that reminded of his father’s voice, and noted how “(Forget About) Georgia,” his song about getting over an old girlfriend, clashed with his singing “Georgia on My Mind” nightly on tour in his dad’s band.

Jamey Johnson (left) and Dave Matthews (right) at the 33rd annual Farm Aid concert

When night fell on the Hartford amphitheater, the Farm Aid principals took over, putting weight behind the term headliners. Dave Matthews and guitar foil Tim Reynolds tapped their Dave Matthews Band repertoire, and even if their dual acoustics lacked some of the tones and drive of that full group, they dug into extended, rhythmic drones in the pertinent “Don’t Drink the Water.” They also went beyond hits with the inclusion of fan favorite “#41” by request of a caterer and “Come Tomorrow” simply because, Matthews noted, it includes a reference to farmers.

John Mellencamp delivered a tough, impassioned set of his best known songs — “Small Town,” a solo acoustic “Jack and Diane” (where he chiding the crowd for coming in too early for the chorus) and “Pink Houses,” with its rousing “Ain’t that America” refrain – as well as “Easy Target” about today’s socio-political tremors. He also changed up the back-screen visuals from the mostly colorful natural images that dominated the day to an ominous storm for “Rain on the Scarecrow.”

The night still belonged to the ornery Neil Young, 72, in his first area appearance with an electric band since 2012, though he donned an acoustic guitar for “Tell Me Why,” “Field of Opportunity” and mid-set nugget “Heart of Gold.” Young also uncorked “Children of Destiny,” a new song with Promise of the Real, singing “Stand up for what you believe, resist the powers that be.” And for fans itching to hear him cut loose on his black Les Paul, Young dropped “Powderfinger” and an 11-minute, guitar-gnashing breakdown of “Love and Only Love” to top the set.

Willie Nelson offered a relative cooldown to close the show with tried-and-true standards like opener “Whiskey River,” “Still is Still Moving to Me” and “On the Road Again,” backed by his Family band including pianist sister Bobbie and sons Micah and Lukas, who injected a decent Stevie Ray Vaughan impersonation on “Texas Flood.” At 85, the grizzled Nelson still flashed facile, jazzy leads on his battered, gut-stringed acoustic and sang “Always on My Mind” like a bittersweet coda. He remains an American treasure, much like the culture that Farm Aid champions.