Colorado is the fourteenth state to allow the immigrants who graduate from state high schools to attend colleges at the lower tuition rate. This month, a similar proposal was signed into law in Oregon. Texas was the first pass such a measure in June 2001.
Hickenlooper signed the bill at the Metropolitan State University of Denver as several hundred students, lawmakers and school officials watched.
"This first step is going to be the first step to national immigration reform," he said.
The bill allows students who graduate from Colorado high schools to attend college at the in-state rate, regardless of their immigration status. To qualify, students must also sign an affidavit saying they are seeking, or will seek, legal status in the U.S.
The out-of-state rate immigrants in Colorado have been required to pay is sometimes more than three times higher than the in-state rate.
Twenty-one-year-old Oscar Juarez, originally from Mexico City, has attended Metro State for two semesters. He moved to Colorado from Arizona after lawmakers there passed a strict immigration enforcement law a few years ago.
"Now, being able to pay less, it's a lot easier, a lot less stressful," he said.
Juarez said he's seen the opinions of the public and Colorado lawmakers change in recent years.
"We saw the hatred from people, we've seen it go down," he said. "They're actually comprehending."
The bill signing comes a decade after lawmakers first tried to pass the measure, which in the past has been opposed by both parties. This year, Democrats unanimously supported the bill and a handful of Republicans joined them.
Other states that allow in-state tuition for immigrants in the country illegally include California, Utah and Connecticut.