Arizona facilities are housing 1,654 immigrant children, including 328 who were separated from their families at the U.S.-Mexico border.
The office of Republican Gov. Doug Ducey confirmed the figures Wednesday.
Ducey says he doesn't think children should be separated from their families but he also wants strong border security.
He urged Congress to take action, saying lawmakers have been talking about legislation "for the last decade."
He added: "They haven't been able to get anything done. Now's the time to act."A nonprofit group has set up a website to help locate immigrant parents and children in U.S. detention facilities as advocates seek to reunite families separated on the southwest border.
California-based Freedom for Immigrants runs a visitation network and hotline for immigrants in detention.
It launched the online form Wednesday where immigration attorneys, advocates and family can input information about immigrants they are trying to find in U.S. government custody.
Group co-founder Christina Fialho says immigrant advocates will granted access to the data and will be able to log their own updates to help sort out more quickly where parents and children being held.
Immigration authorities have an online detainee locator. Fialho says detainees sometimes can't be found there — for example, when they being transferred to a new facilities.