MANCHESTER, Ky. — When smoking first swept the United States in the early decades of the 20th century, it took hold among the well-to-do. Cigarettes were high-society symbols of elegance and class, puffed by doctors and movie stars. By the 1960s, smoking had exploded, helped by the distribution of cigarettes to soldiers in World War II. Half of all men and a third of women smoked.

But as evidence of smoking’s deadly consequences has accumulated, the broad patterns of use by class have shifted: Smoking, the leading cause of preventable death in the country, is now increasingly a habit of the poor and the working class.

While previous data established that pattern, a new analysis of federal smoking data released on Monday shows that the disparity is increasing. The national smoking rate has declined steadily, but there is a deep geographic divide. In the affluent suburbs of Washington, only about one in 10 people smoke, according to the analysis, by the Institute for Health Metrics and Evaluation. But in impoverished places like this — Clay County, in eastern Kentucky — nearly four in 10 do.

“It’s just what we do here,” said Ed Smith Jr., 51, holding up his cigarette in a hand callused from his job clearing trees away from power lines. Several of his friends have died of lung cancer, and he has tried to quit, but so far has not succeeded.