A record 125 people were exonerated last year in the U.S. after being falsely convicted of crimes, according to a new report. The number surpasses the previous record of 91 set in 2013.

Much of the increase was due to one county in Texas. Thirty-three people in Harris County had their drug convictions thrown out after lab tests found they tested negative for the presence of illegal substances.

The report noted that almost all exonerations for drug crimes across the U.S. last year were for convictions based on guilty pleas.

The National Registry of Exonerations, a project of the University of Michigan Law School, credited the rise in exonerations to the nation's 15 prosecutorial Conviction Integrity Units. As NPR's Laura Sullivan explained last year, these are government units "with the sole function of reviewing old cases and ensuring that the agency got it right."

"The big story for the year is that more prosecutors are working hard to identify and investigate claims of innocence," Michigan law professor Samuel Gross, editor of the National Registry of Exonerations and the author of the report, said in a statement. "And many more innocent defendants were exonerated after pleading guilty to crimes they did not commit."

The states with the most exonerations in 2014 are Texas with 39, New York 17, Illinois and Michigan with seven each, Ohio with six, North Carolina with four — and Louisiana, Maryland, Oregon, Pennsylvania and Tennessee with three each. These states are not necessarily those where most false convictions have occurred, the report said.

Nearly 40 percent of those exonerated were exonerated for crimes to which they had pleaded guilty, the report said. It added that non-DNA exonerations had increased.

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