Recently, we reported on the importance of counties in the United States.

Today we have a lot more on what the U.S. Census Bureau calls "the primary political and administrative divisions of states."

There are more than 3,000 counties nationwide.

Most states use the word "county" to describe these subdivisions, or separate areas, within a larger territory. Naturally, there are exceptions to this definition. For example, the southern state of Louisiana is divided up into parishes.

The Census Bureau reports that 1,653 counties lost population between 2010 and 2015. That is more than half of all counties nationwide. At the same time, the general population grew by about 4 percent.

Delaware and Hawaii are the only two states that did not have a single county with a falling population number.

If not for new immigrants, 194 more U.S. counties would have lost population.

More people are dying than are being born in more than one-third of all counties. Population experts call this "natural decrease." But that does not always mean their population is shrinking.

A county's population can grow even when there are more deaths than births. The reason? People are moving there from other parts of the United States or from other countries.

Some news stories have described counties that record more deaths than births as "dying counties." In 2009, the Census Bureau reported natural decrease in 880 counties. In 2012, the Census Bureau estimated natural decrease in 1,135 counties. Most were in rural areas.

Kenneth Johnson is a professor of sociology at the University of New Hampshire. He told the Associated Press that the number of counties with natural decrease is rising not only because there are fewer births than deaths in those areas. He said another reason is an increase in the number of deaths among "baby boomers." The term baby boomer is used to describe the 70 million Americans who were born between 1946 and 1964.

Johnson said, "I expect natural decrease to remain high in the future. These counties are in a pretty steep downward spiral. The young people leave and the older adults stay in place and age."

He adds, "that unless something major changes -- for instance, new development such as a meatpacking plant to attract young Hispanics -- these areas are likely to have more and more natural decrease."

About 46 percent of rural counties experienced natural decrease. That compares to 17 percent of counties in populated areas.

Experts say counties "die" because they have increasingly-older populations, a low birth rate and a poor economy. They say it is difficult for some areas to retain or attract younger people.

Japan and many European countries have been experiencing natural decrease for many years.

In the United States, the 10 largest counties are in the West, in states such as California, Arizona and Nevada. Some of the smallest counties are in eastern states.

The first counties were created in Virginia in the 1630s. Maryland and Massachusetts established counties a short time later.

The Census Bureau says there are 3,031 counties nationwide. But the National Association of Counties (NACo) says there are 3,069. Association officials told VOA they use the term "counties" for both county governments and county geographies with county governments.

Five of the 10 smallest counties by population are in the state of Nebraska. Cook County, Illinois, which includes Chicago, is the second-most-populous county in the nation. It has more people than 29 states and more than the seven smallest states combined.

The top four most densely populated counties are in the New York City area. The top four least densely populated counties are in Alaska.

Some cities and counties have joined together. In other words, the city and county are controlled by one government. These include the city and borough of Anchorage, Alaska and the city and county of San Francisco, California; Denver, Colorado; Baltimore, Maryland and St. Louis, Missouri. Yet the state of Virginia has 39 independent cities that are not part of any county.

Generally, county governments are strongest in the western and southern United States, and weakest in the east, where there are more cities. Few counties create laws like state legislatures and city councils do. Most just enforce state laws.

There are about 3.6 million county government employees in the United States.

About a third of counties operate hospitals. Counties are involved in 27 percent of public transportation systems and 34 percent of public airports. They own 40 percent of the bridges, and own and repair 45 percent of the roads.

And that's all we have today about U.S. counties.

I'm Anna Matteo.

And I'm Christopher Jones-Cruise.

VOA's Christopher Jones-Cruise reported this story from Washington. George Grow was the editor.