Long Island's immigrant population not only has continued to grow in size and diversity, but also is having a significant impact on the region's economy, according to a new analysis of census and other demographic data to be released Tuesday.

About 526,000 people born outside the United States live in Nassau and Suffolk, making up 18 percent of the Island's 2.9 million people and powering the region's labor force, according to the study by the Fiscal Policy Institute, a progressive nonprofit in Manhattan that studies tax and budget issues.

Those immigrants account for about 20 percent of economic output -- that's $18 billion out of $91 billion in combined earnings from work and business, making up a fifth of such wages and profits in the two counties, according to the study. The analysis focuses largely on 2013 figures from the U.S. Census Bureau, updating similar findings from 2009.

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Study author David Dyssegaard Kallick, a senior fellow with the institute, said the figures show immigrants are vital to the region's future. The study was funded by the Port Washington-based Hagedorn Foundation, which backs immigrant-advocacy efforts.

"Given the political climate, I think it's maybe surprising to see just how substantial an economic contribution immigrants are making and just how varied immigration on Long Island is," Kallick said.

"There's both a significant increase in the immigrant share of the population and a corresponding increase in the economic contributions of immigrants" since 2009.

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The study paints a nuanced portrait of immigrants here as a diverse crowd of largely legal residents or U.S. citizens who aren't always toiling in low-wage jobs. El Salvador, India and the Dominican Republic top the countries of origin.

The population of immigrants here illegally is about 98,000, based on an estimate used for this analysis that combines different surveys. Close to half the unauthorized immigrants hail from Central America.

Source: Migration Policy Institute

News of the Indian community's growth came as no surprise to nine men trading stories and jokes in English, Hindi and Punjabi on a recent afternoon at a seniors' group meeting at the India Association of Long Island in Hicksville.

Mohan Sharma of Syosset said he and his wife came from New Delhi last year to join their son, a bank employee who came here seeking work, then married and started a family. "Where our son lives, we have to live," said Sharma, 67, who struggles to speak English and said he would like to see more Hindi interpreters in businesses and public offices.

Vijay Goswamy, 69, co-chair of the seniors group and a retired hospital administrator, remembers when he was among a small community of Indian immigrants on Long Island in the late 1970s. "Before, if you saw an Indian you would grab him to have someone to talk to. Now, I see one and keep going and think, 'I have enough friends.' "

Indians exemplify trends highlighted in the analysis: More than half the foreign-born residents are working in white-collar jobs, while six of every 10 immigrant households report incomes of more than $80,000 per year. About three-quarters live in owner-occupied housing.

On average, the region's immigrants earn 31 percent less than U.S.-born workers.

The earnings figures do not tell the whole story about immigrants' impact, said Steven Camarota, research director of the Center for Immigration Studies, a Washington, D.C., group that favors stricter immigration controls. Camarota said 41 percent of immigrant households in New York used one or more "welfare programs" in 2011, including food assistance, public housing, Medicaid and cash help.

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"The Indian doctor makes a lot more here than he would make in India and so would the Chinese engineer," he said. "But if you want to know the answer to the big question -- what's the fiscal balance? -- this study is not telling us that."