The United States has more immigrants than any other country in the world. Today, more than 40 million people living in the US were born in another country, accounting for about one-fifth of the world's migrants. Also, the population of immigrants is very diverse, with just about every country in the world represented among US immigrants. Pew Research Center regularly publishes statistical portraits of the nation's foreign-born population, which include historical trends since 1960. These portraits provide more details on the US immigrant population. The US foreign-born population reached a record 44.8 million in 2018. Since 1965, when US immigration laws replaced a national quota system, the number of immigrants living in the US has more than quadrupled. Immigrants today account for 13.7% of the US population, nearly triple the share (4.8%) in 1970. However, today's immigrant share remains below the record 14.8% share in 1890 when 9.2 million immigrants lived in the US. Most immigrants (77%) are in the country legally, while almost a quarter are unauthorized, according to new Pew Research Center estimates based on census data adjusted for undercount. In 2017, 45% were naturalized US citizens, 27% of immigrants were permanent residents, and 5% were temporary residents in 2017. Another 23% of all immigrants were unauthorized immigrants. From 1990 to 2007, the unauthorized immigrant population was more than tripled in size – from 3.5 million to a record high of 12.2 million in 2007. By 2017, that number had declined by 1.7 million, or 14%. There were 10.5 million unauthorized immigrants in the US in 2017, accounting for 3.2% of the nation's population. The decline in the unauthorized immigrant population is due largely to a fall in the number from Mexico – the single largest group of unauthorized immigrants in the US.