Singer used the money to bribe officials at various schools, including Georgetown, Stanford, UCLA, USC, the University of San Diego, the University of Texas, Wake Forest, and Yale.
Under the guise of a non-profit company that helped students with their college admissions, Singer would pay to have SAT and ACT tests retaken or scores changed, and also for students to be accepted through athletic programs in sports they didn't actually play.
John Vandemoor, a former Stanford University sailing coach who worked with Singer, also pleaded guilty to racketeering conspiracy.
Huffman and Loughlin, as well as her husband Mossimo Giannulli, were identified as being contributors in a scheme in which wealthy parents allegedly bribed college coaches and other insiders to get their children into some of the nation's most selective schools.
Huffman allegedly gave $15,000 "to participate in the college entrance exam cheating scheme on behalf of her oldest daughter", the indictment in the case states. She, along with Full House actress Lori Loughlin, are accused of participating in a scheme along with other elite parents to scam their children into prestigious universities using false information.
"For every student admitted through fraud an honest, genuinely talented student was rejected", he added.
Federal prosecutors in Boston charged William "Rick" Singer, 58, with running the scheme through his Edge College & Career Network, which charged from $US100,000 to as much as $US2.5 million per child for the services, which were masked as contributions to a scam charity Singer runs.
Dick Cheney Compares Trump's Foreign Policy to Obama's
In a private session, the former vice president told the current one that Trump's policy looks too much like Barack Obama's. The debate took place during Cheney's interview of Pence for those in attendance.
During her hearing on Tuesday, Macy remained by her side.
Nine college coaches, two SAT/ACT administrators, one test proctor, one administrator, and 33 parents are now facing charges.
They're accused off illegal greasing hands to get their kids into school. Huffman spent hours in federal custody at a detention center in downtown Los Angeles. Several of the colleges involved made no mention of taking any action against the students.
Authorities have called it the biggest college admissions scam ever prosecuted by the US Justice Department - with parents accused of paying an estimated $25m (€22m) in bribes.
Huffman is scheduled to appear in federal court in Boston on Friday, March 29.
"These parents are a catalogue of wealth and privilege", prosecutor Andrew Lelling said in announcing the 25 million dollar (£19 million) federal bribery case.