A new report is showing a decline in the population of undocumented immigrants in Colorado. A study by the nonpartisan Pew Research Center was released yesterday. It shows the amount of undocumented immigrants in Colorado dropped from around 210-thousand in 2007 to about 180-thousand in 2017. The figures reflect a nationwide decline during that time period. Experts say factors for the drop include changes in border enforcement and the U.S. economy.