Fairfax County is getting older. Fewer young people and more older people live in the county now than 10 years ago.

As the county ages, it is also becoming more diverse. There are more females and more blacks and other minorities living in the county now than 10 years ago.

Matching national trends, divorces granted in the county have increased greatly in 10 years, and the birthrate has dropped steadily.

These are the findings of a recent demographic study done by Fairfax County's Office of Research and Statistics in an effort to identify growth patterns in one of the nation's wealthiest counties.

The study, the second population outline done by the office, projects that these same trends will continue in Fairfax County for the next 20 years.

"Fairfax County is going to be changing from a primarily white, young county with few elderly people to one that is older and that has a wider variety of people," said David Sheatsley, county demographer who helped prepare the report. "In other words, Fairfax County in 20 years will approximate the character of Montgomery County now."

The report is intended to be used as an infomation source for families and businesses moving into the county and as a general planning tool for county staff.

The report says that in 20 years the county's median age - now about 26 years, one of the youngest in the metropolitan area - will increase to slightly more than 30 years.

"Four years doesn't sound like a big jump," Sheatsley said. "But a lot of forces have to combine for an increase like that, including a decline in births, a shift in current family structures and a tendency for fewer young people to move in."

Because the county will have fewer people younger than 19 years old, the county's working force will have fewer dependents, the report says.

"This probably means that Fairfax County residents will be able to afford more, but that goods and services are going to cost more," Sheatsley said.

With a continually declining youthful population, fewer educational facilities should be needed in the county, the report suggest. The report does not indicate population changes in individual districts, however, to pinpoint areas where schools will either be needed or unnecessary.

In 20 years, 13 per cent of the county's population will be 55 or older, which indicates more services for senior citizens will be needed.

The rapidly increasing number of divorces granted yearly in the county reflects a need to change housing trends, Sheatsley said. He added that it also indicates Fairfax County is losing its "family characteristics."

The county granted 716 divorces in 1967 and 2,522 last year, the report shows. If this trend continues, the county will need to provide smaller housing units than are currently being built.

Sheatsley said a recent housing study showed that housing units being built in the county are getting larger, rather than smaller, and that population trends "may influence the housing industry to start building smaller homes."

Concerning other demographic changes in Fairfax County, the report showed that:

The number of blacks in the county, now about 5 per cent of the total population, will increase to about 8 per cent in 20 years, and the percentage of other minorities, now 1.5 per cent, will continue to increase slowly and steadily to 1.7 per cent within 20 years. Minorities other than blacks comprised less than 1 per cent in 1960.

The county's birth rate has declined from 24 per cent in 1960 to about 14 per cent.

The infant mortality rate has dropped from about 17 per cent to about 13 per cent in 10 years, while the death rate for the population as a whole has remained stable.