PHOENIX — The number of people in this state illegally dropped by close to 12 percent between 2009 and 2012 according to a new study.

But despite the drop, more than 121,000 students in public schools in Arizona is the child of at least one parent who is not here legally.

Probably close to 97,000 of those were born in this country and are U.S. citizens. But the data suggests that they would not have been born here — and enrolled in Arizona schools — had one of their parents not entered the country illegally or overstayed a visa.

And the balance of those 121,000 were not born in this country and are themselves undocumented.

The study comes amid reports the Obama administration is planning to use executive action to provide some sort of protected status for at least some of the 11.2 million people in this country who are not authorized to be here.

That is on top of the approximately 675,000 who already been accepted into the government's Deferred Action for Childhood Arrivals program. It allows those who arrived as children and meet other qualifications to not only remain without fear of deportation but also to work legally.

In Arizona, close to 25,000 had qualified for DACA at last count.

Overall, Pew Hispanic estimates there are now only about 300,000 unauthorized immigrants in Arizona, down by about 40,000 from 2009. And that represents a 40 percent drop from 2007, when the undocumented population peaked here at about 500,000, before the recession dried up many of the work opportunities.

But the decrease here is not unique — and may be unrelated to anything done at the state level, including the 2010 approval of a tough new law designed to give police more power to question those they suspect are not here legally.

The Pew study shows a drop in 14 states, most of them in the Southwest. And the report says that is due to a combination of more Mexicans leaving, whether voluntarily or not, and fewer coming to this country.

But there is a separate trend taking place elsewhere: Pew Hispanic finds seven states where the unauthorized population actually increased. In that case, however, the report says that was due to an increase in the number of people from countries other than Mexico.