A number of undocumented immigrants in the United States has been high and stable for the last decade, having little difference with the 2007 migrant peak, a new preliminary estimate by Pew Research Center revealed Wednesday.

MOSCOW (Sputnik) — Some 11.3 million undocumented immigrants lived in the United States in 2014, while 12.2 million were registered in 2007 which was considered a peak in the last two decades, an estimate revealed.

"The overall estimate has fluctuated little in recent years because the number of new unauthorized immigrants is roughly equal to the number who are deported."

The latest undocumented immigrant total includes those who have crossed the US border illegally, as well as those who arrived with legal visas and remained in the United States after their visas expired, the study stressed.

Since 2009, some 350,000 new undocumented immigrants have been arriving in the United States annually, the Pew Research estimated.

A number of immigrants from Mexico to the United States has been relatively high since the early 1990s, amounting to more than a half of the total, but in recent years declined nationwide — some 5.9 million immigrants from the bordering Mexico lived in the United States in 2012 which about a million fewer than in 2007, Pew Research Center said.

Meanwhile, many more people from other countries attempted to cross the US border illegally, the study has found.

According to the Migration Policy Institute, the current number of US immigrants and their US-born children amounts approximately to 80 million people, which one-quarter of the overall population of the country.