The overall percentage of lawful immigrants gaining U.S. citizenship is the highest it has been in two decades, but a newly released survey by the Pew Research Center found that Mexican legal residents are among the least likely to naturalize.

In 2015, Mexican immigrants accounted for more than a third of the 9.3 million immigrants who could apply for U.S. citizenship, making them the single largest origin group among those eligible to naturalize. However, while the naturalization rate among Mexicans had risen to 42 percent that year, for non-Mexicans it had risen to 74 percent.

Researchers found Mexican immigrants are more likely than other groups to cite barriers to naturalization, despite the fact that 98 percent of Mexican legal residents expressed a desire to become U.S. citizens.

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When asked why they had not yet naturalized, 35 percent of Mexicans identified personal barriers, such as a lack of English proficiency, and 13 percent cited financial and administrative roadblocks.

In terms of specific barriers to naturalization, Mexican lawful immigrants and those of non-Mexican origin provided similar reasons. However, about a third (31 percent) of Mexican immigrants cited a lack of interest or having not applied yet as reasons for not naturalizing, as compared to 16 percent of non-Mexican immigrants.

According to Pew Research, about two-thirds of eligible immigrants had applied and obtained citizenship in 2015, the highest share since the mid-1990s.

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