On Thursday, Immigration and Customs Enforcement (ICE) spokesman Bryan Cox told the BBC that, of the 680 people arrested in Wednesday's raids, more than 300 had been released with notices to appear before immigration judges.
"They were placed into proceedings before the federal immigration courts and will have their day in court at a later date," he said in an emailed statement.
The detentions took place at chicken processing plants, owned by five different companies, in the towns of Bay Springs, Canton, Carthage, Morton, Pelahatchie and Sebastopol.
Those who were not released will be moved to an ICE detention facility and held there, Cox said.
Cox told the BBC that those arrested were asked if they had any dependents needing care or if they had any children at school who needed to be picked up.
They were given access to phones at the processing site to make arrangements to care for their children.
He said those with child care issues were "expeditiously processed and returned".
About 30 of the people detained were released on humanitarian grounds, the US Attorney's Office for the Southern District of Mississippi said.
The ICE did not share details about the nationalities of those detained, but the Mexican government has reportedly sent consular staff to the area to help any of their nationals who might be involved.
( With inputs from IANS )