In Caribou, Maine, a town of 7,400, the splash pad was packed with children at noon on Wednesday as temperatures soared. But next to it, at a cooling center for the rural area’s many elderly residents, all the folding chairs were empty, even though three air-conditioners were blasting a frigid breeze.

Officials had spread the word across Aroostook County about the cooling center on social media, on radio stations and TV, and in local newspapers. However in Maine, and across wide areas of rural America, the techniques familiar in cities to help people beat the heat are much more difficult to carry out effectively.

“But we’re here,” said Gary Marquis, the superintendent of the Caribou Parks and Recreation Department.

Large parts of the nation were boiling this week as temperatures climbed in Maine and other areas that are not accustomed to mid-June heat waves. In many cities, residents cooled off in shady parks, jumped in public pools, or hydrated with cold water handed out by paramedics and police officers stationed at busy intersections or inside public transportation hubs — all tactics health officials encourage to help avoid heat-related illnesses.

These kinds of strategies are common in countless cities because they are effective in areas with large populations. In more rural areas, however, people are far more spread out and much harder to reach.

“We’re missing a large swath of our society, and a swath that typically has higher levels of chronic disease, older populations and lower income,” said Kevin Lanza, an assistant professor of environmental science at UTHealth Houston in Austin. “All three are factors increasing the serious risk on rural communities in the face of climate change.”