Researchers also predict that the gap will become even wider in the future; during the period studied—1980–2014—11.5 percent of U.S. counties saw the risk of death for residents aged 25–45 increase. No previous study, the report says, “has put the disparity at even close to 20 years.”

Says The Guardian, “Previous studies recorded lower variations ranging from 12 to 17 years between counties, with the highest and lowest life expectancies in both 2007 and 2010. These were an underestimation, according to the University of Washington team, because data from smaller counties was either combined with others or excluded altogether.”

“This is way worse than any of us had assumed,” Ali Mokdad, professor of global health at the University of Washington's Institute for Health Metrics and Evaluation and one of the authors of the study, is quoted saying in the report.

He adds, “You expect disparities in any country, but you don't expect the disparities to be increasing in a country with our wealth and might. We spend more money on healthcare than anybody else, and we debate the hell out of healthcare more than anybody else, and still the disparities are increasing.”

Mokdad points to the dispute in Congress over health insurance as an example of how misleading the mere coverage by a health insurance policy can be, and how indicative it is of inequality.

“Many people don't have health insurance, but even among those who do it's misleading,” he says in the report, adding, “My insurance, for example, allows me to go to a doctor for an exam and a blood test and they'll tell me if I have a problem early on. Many don't have that luxury, only catastrophic insurance, so if they're hit by a car they'll be treated.”

He also highlights how location can play a role in other health factors, such as those who live in mountainous or rural areas where it can take two hours to reach a good health facility in the event of an emergency—or the poor areas within or just outside of rich cities that are food deserts for such essentials as fresh produce.

The study calculates overall average U.S. life expectancy at 79.1 years, 5.3 years higher than in 1980—which is the beginning of the 35-year period for which researchers compared death records, census returns, the human mortality database and figures from the National Center for Health Statistics on a county-by-county basis.

However, researchers caution that that 5.3-year increase “masks massive variation at the county level,” adding.

They added, “Counties in central Colorado, Alaska and along both coasts experienced much larger increases, while some southern counties in states stretching from Oklahoma to West Virginia saw little, if any, improvement over this same period.”

When it came to decline, variation again was key.

Researchers write, “Similarly, there was considerable variation among counties in the percent decline in the mortality risk within each age group. While all counties experienced declines in mortality risk for children 0 to five years, and nearly all experienced declines in the mortality risk for adolescents and older adults 45 to 85, 11.5 percent [of counties] experienced increases in the risk of death between ages 25 and 45 years.”

Where does the variation come from?

The study points to differences in socioeconomic and race/ethnicity factors, availability of and access to quality health care and insurance, and “preventable risk factors” such as smoking, drinking and physical inactivity.

But other factors cause problems, too, such as guns, automobile accidents and drugs, which weigh on male lifespans, as well as the availability of fresh fruits and vegetables in local markets and people's distance from health care providers—factors over which they have little or no control.

Below you'll find the 7 states in which counties have the longest lifespans or have experienced the greatest increase in life expectancy, as well as the 7 states in which counties have the lowest lifespans or have experienced the greatest decrease in life expectancy.

The states are not in order, and you'll notice something interesting as you go through both lists:

7 regions in the U.S. with the longest life expectancy

7. Minnesota.

Southern Minnesota boasts several counties where the length of lifespan is quite impressive.

6. Colorado.

Colorado offers some really impressive longevity statistics, although most of the counties accounting for that are mostly located in the central portion of the state.

5. Wyoming.

If you follow the admonition to “go west, young man,” you'll find the majority of the Wyoming counties offering the best chance at a lengthy life.

4. Texas.

Again, the western part of the state houses most of the counties where residents live longest—although there have been less notable gains in some other parts of the state.

3. California.

Everyone flocks to the coast in California, and the majority of the counties offering the chance for the longest life in the state are coastal counties.

2. Florida.

Southwestern Florida offers residents the best chance at a long life, having experienced a substantial increase in longevity over the period of the study.

1. Alaska.

Some Alaska counties saw major increases in lifespan between 1980 and 2014.

7 regions in the U.S. with the lowest life expectancy

7. North Dakota.

North Dakota and its neighbor to the south have the dubious distinction of having counties with the lowest life expectancy—nothing to boast about.

6. South Dakota.

South Dakota shares the misfortune with North Dakota of having counties offering the lowest life expectancy.

5. Oklahoma.

Southern counties in a number of states, including Oklahoma, saw little or no improvement in lifespan over the course of the study period.

4. Mississippi.

Rural western Mississippi is home to counties that do very poorly when it comes to longevity—and they haven't experienced much, if any, improvement over the life of the study.

3. Kentucky.

Eastern Kentucky is another state in which a number of counties suffer from shorter lifespans.

2. West Virginia.

Southwestern West Virginia is another area where counties are suffering.

1. Alaska.

Yes, Alaska actually makes both lists—while counties experienced substantial increases in lifespan over the period of the study, life expectancy at birth across the state is nothing to boast of.