Prosecutors have so far named 33 parents, 13 coaches, and associates of Singer's business.
Some parents spent hundreds of thousands of dollars, as much as $6.5 million, to guarantee their children's admission, officials said.
The Emmy victor, 56, was among 46 wealthy folk whom the authorities said had resorted to fraud, bribes and lies to get their children admitted to elite colleges.
"The department is looking closely at this issue and working to determine if any of our regulations have been violated."
Mr Giannulli was released on $1 million bail.
She is expected to appear in a Boston court on March 29 for a preliminary hearing.
He was released on $US500,000 bail by a federal magistrate who overruled a federal prosecutor's objection to Mr Hodge keeping his passport.
Loughlin returned home to Los Angeles Wednesday to surrender to US federal authorities.
Huffman was arrested at her home by armed Federal Bureau of Investigation agents and was later released on bail after her husband, Shameless actor William H.
William "Rick" Singer, 58, pleaded guilty in Boston federal court on Tuesday to running the largest college admissions fraud scam in US history through his small college preparation company in Newport Beach, California.
Tucker Carlson's words reveal who he really is
And so going forward, we'll be covering their efforts to make us be quiet", Carlson said of his detractors Monday night. On that same appearance, he called Alexis Stewart, a television and radio host and daughter of Martha Stewart, "cunty".
Prosecutors called it the largest such scandal in United States history.
U.S. attorney Andrew Lelling said: "These parents are a catalogue of wealth and privilege". None of the children were charged on Tuesday. Stanford fired the sailing coach, and USC dropped its water polo coach and an athletic administrator.
The FBI says actress Lori Loughlin has been taken into custody in connection with a scheme in which wealthy parents paid bribes to get their children into top colleges.
Court documents allege that Felicity Huffman, 53, paid $15,000 to secure her eldest daughter a place at university. Her husband, designer Mossimo Giannulli, appeared in court on Tuesday, as did Felicity Huffman.
Loughlin and Giannulli have two daughters, Isabella Rose, 20, and YouTube star Olivia Jade, 19.
'I was essentially buying or bribing the coaches for a spot, ' Singer said as he pleaded guilty to charges on Tuesday.
The bribes allegedly came through Singer's admissions consulting company, Edge College & Career Network.
After months of having his calls wiretapped, Singer ended up cooperating with investigators last September, helping them secretly record incriminating conversations he had with parents.
The consultant also hired ringers to take college entrance exams for students and paid off insiders at testing centers to correct students' answers, they said. Singer allegedly helped parents "take staged photographs of their children engaged in particular sports", and in other instances used stock photos by "sometimes Photoshopping the face of the child on the athlete, and submitting it".
Her attorney declined to comment. Several of the coaches accused of accepting bribes have been fired, placed on leave or have resigned.