"They even want to try to rig the election at the polling booths and believe me there's a lot going on," he added, according to Talking Points Memo.
The Republican presidential candidate alleged that the Democrats and Hillary Clinton campaign were actively coordinating the widespread voter fraud and rigging.
Talking Points Memo suggested that Trump may have derived the figure of 1.8 million dead people voting from a 2012 Pew Study that reportedly found that about 1.8 million active voter registrations were deceased persons. But the study concluded that the registrations were not due to fraud or dead people casting ballots but state voter databases that were not updated.
Trump also cited an article by the Washington Post to back his claim that illegal immigrants were voting across the country.
According to the article, authored by two political scientists, enough non-citizens voted in 2008 to influence the outcome of the presidential election in North Carolina, which President Barack Obama won by 14,000 votes.
"It is possible that non-citizen votes were responsible for Obama's 2008 victory in North Carolina," Trump reportedly said. "Obama won this state by 14,000 votes... we are going to win in North Carolina, but we don't want non-citizen voters... It could have provided his [Obama's] margin of victory."
But the Huffington Post noted that several experts faulted the claim by the two political scientists, saying it was based on unreliable data gathered from an online survey that relied on voluntary participation rather than random sampling used in scientific polling.
Trump's latest statements come after previous multiple allegations that the Democratic Party was rigging the election in major urban areas.
However, Politfact, which scored Trump's claim of widespread "voter fraud" and "rigging" on the "Truth-O-Meter" as "pants on fire," noted that despite his allegations, multiple independent studies and surveys have found no evidence of planned or orchestrated voter fraud and rigging occurring at a significant level.
Most cases of irregularities in voter registration were found to be due to clerical errors, outdated registration records, poor record keeping, and management rather than deliberately orchestrated voter fraud.
Politifact cited a well-known case of what was thought to be a dead person voting but which turned out to have been due to the polling clerk misspelling the name of a voter.
According to Politifact, cases of deliberately orchestrated voter fraud and rigging are very rare, indeed. They are too rare and limited to have had a significant impact on polling results in the past.
Despite widespread criticism, Trump repeated his initial statements alleging fraud and rigging with a tweet on Sunday.
"The election is absolutely being rigged by the dishonest and distorted media pushing Crooked Hillary -- but also at many polling places -- SAD," he said.