One in 5 people in Riverside County lacks basic English literacy skills, according to data released Thursday by federal education officials.

The estimate is based on information about adult literacy that the National Center for Education Statistics collected in 2003.

It wasn't until recently that the center, a federal agency that gathers and analyzes education-related data, broke down the numbers to the state and county level.

In Riverside County, 20 percent of people ages 16 or older are functionally illiterate, the data shows.

That percentage is double what it was only 11 years ago. At that time, the center estimated that only 1 of every 10 people in the county was illiterate.

The increase appears to be related to immigration, said Debra Jones, director of adult education for the California Department of Education.

Counties that have experienced a significant amount of immigration show lower literacy rates, she said.

In 1990, Riverside County had 173,754 immigrants who made up nearly 15 percent of the population, according to U.S. Census data.

By 2000, the number of immigrants in the county had grown to 293,712, or 19 percent of the total population.

The illiteracy numbers include people who don't speak English, but who may be able to read and write in another language.

The numbers released Thursday were not at all surprising, said Melodie Earickson, adult literacy coordinator for Riverside County's southwest region.

"In fact, I think that's more positive than what I've heard in the past," she said.

Adult illiteracy is linked to unemployment, crime and poverty, according to the National Institute for Literacy.

California had the highest illiteracy rate of any state, with 23 percent of people lacking basic skills in 2003, up from 15 percent in 1992.

Jones said she thinks the numbers are accurate and reliable, but that they were a bit shocking.

The center decided to compile the state and county estimates to help educators and politicians set priorities for local literacy programs, officials said.

Information is available only for 1992 and 2003. Officials with the center said they don't expect another study until 2016.

People considered lacking basic literacy skills ranged from those who can't read at all to those who can locate some simple information in text, but nothing more advanced.

Schools and libraries throughout Riverside County are offering similar programs to help people boost their literacy skills or learn English.

In Temecula, the library runs two classes for people learning English. Local libraries also offer tutors for native English speakers who need help boosting their reading skills. Both services are free.

Though the area has grown over the last several years, Earickson said, the number of people volunteering to tutor and asking for assistance have decreased.

Most people who come for help usually do so because an employer has told them to brush up on their language skills or because they're hoping to get a better job, Earickson said.

Some also want to be able to better help their children with homework, she said.

"If they're not able to help their children," she said, "their children are not going to have the advantages and opportunities as literate adults."

Although people sometimes go to great lengths to hide their illiteracy and are reluctant to ask for help, when they do, they're usually very enthusiastic, Earickson said.

"It's a great relief when someone finds out that they're going to be able to learn to read," she said.

The literacy rate for San Diego County was about the same, with 21 percent of people 16 or older functionally illiterate, the data showed.

But just because people don't have basic literacy skills doesn't mean they can't read, said Carrie Scott, literacy coordinator for Carlsbad Library's learning center. Rather, those who are functionally illiterate often have major holes in their understanding of the language, she said.

"It's actually very rare that we see someone who can't read or write at all," she said.

Contact staff writer Stacy Brandt at (951) 676-4315, Ext. 4009, or sbrandt@californian.com.