She was born in Mexico and lives in the United States, but Laura Rocio Ordonez does not officially exist in any country.

She can't open a bank account or get married. She is invisible for both governments. Ordonez, 40, not only lives illegally in the United States but also lacks Mexican identification documents.

It's unclear how many immigrants living illegally in the United States fall into that category, but it's estimated that one in seven Mexicans lacks proof of birth. The numbers are high enough that Mexican officials recently traveled to New York to try help dozens of immigrants get IDs.

Mexican immigrants living illegally in the United States are in a far worse situation if they lack Mexican credentials.

For example, some banks accept consular identification cards and passports to open accounts. Immigrants with IDs from home also can obtain taxpayer identification numbers that allow them to pay taxes in the United States and obtain credit and mortgages. New York City public schools accept consular ID cards and similar documentation to enter buildings for meetings with teachers, although people who have no identification at all can be escorted inside.

Ordonez, who was born in Oaxaca and came to the United States illegally years ago, is not included in Mexico's birth registry. She thinks her parents did not register her, and she did not solve the problem while she lived in her home country.

She said she can study English but has no hope of obtaining a GED diploma because of her lack of ID.

"I feel helplessness, frustration," said Ordonez, who works at a small grocery store in Brooklyn. "This has affected me greatly."

Officials at Mexico's National Institute of Statistics and Geography and the National Registry of Population and Personal Identification said they have no data on how many Mexicans are not included in the registry, but lack of identity is a common problem in poor and remote towns of states like Oaxaca, Guerrero, Chiapas, Veracruz and Hidalgo, where people have sometimes to walk long distances to find a civil registry office.

About 23 percent of Oaxaca's population is not included in the born registry, according to the state's civil registry office. Oscar Ortiz Reyes, executive director of Mexico's BE Foundation Right to Identity, said that in 2008 "invisible" Mexicans represented 14 percent of the country's population, according to data from the Inter-American Development Bank.

It's hard to determine how many of those people are now in the United States, given the underground nature of illegal immigration.

New York City's Mexican consul, Carlos Sada, estimates there could be hundreds in New York, New Jersey and Connecticut who are not included in his country's registry or who have errors on their birth certificates. He added that there are "considerable figures" of people in the same situation across the U.S.

Oaxaca's civil registry officials recently traveled to New York and spent a week in the city working to give an identity to dozens of immigrants.

Civil registry officials also have traveled to Los Angeles on the same mission, and officials from the states of Puebla and Guerrero will probably come to New York soon, said Mexico's consulate in the city.

Haydee Reyes Soto, director of Oaxaca's civil registry, said Mexicans with no U.S. or Mexican identification are "twice as vulnerable."

Soto said dramatic scenarios can unfold, with immigrants being arrested but with no place to be deported to. If they have children in the United States, they can't offer them Mexican citizenship because they don't have it themselves. That can result in the separation of families.

Lack of identity is a serious problem as states approve their own laws to fight illegal immigration and local police departments work with federal agencies to identify immigrants for possible deportation, said Leticia Alanis, president of La Union, a Brooklyn nonprofit that helps immigrants.

"You need identification for everything," she said. "If a policeman stops you, you need identification. ... We all should have something that says who we are."

Groups like Make the Road New York and El Centro del Inmigrante, on Staten Island, offer ID cards to their members, which sometimes helps immigrants without Mexican identification.

"We ask them to send a letter to themselves and when they receive it, we ask them to bring it to us. Like that, we can check their address," said Gonzalo Mercado, director of El Centro.

Ester Bautista can hardly read or write because she was forced to abandon school in Mexico when she was 10. The Mexican immigrant, who is now 37, said her school asked her for an ID. She did not have any.

"My life would have been better if I had been registered," she said. "I feel unprotected in many aspects."

Bautista, who was born in the small Oaxaca town of Zimatlan de Lazaro Cardenas, said her father was murdered when she was only 2 months old. Her mother was alone and poor. She had no means to travel to another town where the civil registry office was located.

Bautista has never been able to marry her boyfriend, Jaime Garcia. The couple has a 12-year-old son, born in New Jersey. After living in the United States for 13 years, Bautista obtained her birth certificate last month when the Oaxacan officials visited New York.

When they handed it to her, she smiled timidly.

"It is like being born again," Garcia said. "She needed an identity. The first thing we are going to do is get married."

Bautista called her mother to announce the good news.

"She feels so proud of me," she said. "She always felt bad ... because she never registered me."