‘Here they come,” said the security guard, mopping sweat from his brow. He was tall and bald but not imposing, and he worried that the searing heat would lead to too much drinking. It was 3 p.m. on June 11, and the gates to the Ravinia outdoor theater in Highland Park, Ill., had just opened. People streamed in carrying coolers and lawn chairs, checkered blankets and wineglasses, plasticware full of crackers, melons and deviled eggs. They politely competed for swatches of grass in the shade of oak trees mounted with thank you for not smoking signs.

They wore old Cubs shirts and sun hats of all colors. A stuffed bald eagle perched atop one of the coolers. Vendors sold bottles of wine for $40. The security guard’s concerns proved well founded; the Malbec went quickly, then the Moscato. Lawn space dwindled, and with it some of the crowd’s civility. An old man struggled under the weight of two folding chairs. His wife worried aloud that he’d have a heart attack. “Keep walking!” he snapped.

They had come to see Garrison Keillor one last time. The creator and host of “A Prairie Home Companion” had for four decades gently skewered their baby-boomer sensibilities with fake ads for rhubarb pie and stories about family life that descended into jokes about plagues of rats and apocalyptic climate change. “There’s something about this kind of humor people my age can appreciate,” said Tim Balster, a gray-haired magician I met in the crowd. “It’s like a quilt.” Balster had been listening to “Prairie Home” for 33 of his 52 years. He loved nothing more than to hear the aging writer breathing deeply, his nose right next to the mike. “It draws you in,” he said, “like a moth to the flame.”

Now that was ending. Only four shows remained before Keillor would depart, relinquishing hosting duties to a 35-year-old mandolin player from California named Chris Thile, who was appearing as a musical guest for this show. As we sat in the grass, Balster noted that Keillor left the show once before, when he married a Danish woman, only to return. It was true. But this hiatus occurred during the Reagan administration, when Keillor, now 74, was still a relatively young man. Nevertheless, Balster said, “I’m holding out hope.”