Some areas have experienced an influx of non-English speakers in recent years, erecting language barriers for state and local governments to overcome.

As Ryan Holeywell writes in the current issue of Governing, governments have responded to meet the needs of these new residents in a variety of ways. Many communities established liaisons to assist immigrants. Others invested in translators or language training for employees.

Governing analyzed historical census data for each county in the U.S., measuring residents age 5 and up who reported they spoke English “less than very well.” Data from the 2000 Census was compared with American Community Survey estimates compiled from 2006 to 2010, the most recent complete data set comprising all counties.

The resulting map illustrates language assessment for each county in the U.S. To view historical numbers for a particular area, click a county on the map.

It’s not surprising that counties with the most non-English speakers are home to historically large concentrations of immigrants. About a third of residents are not completely fluent in English in Miami-Dade County, Fla., Hidalgo County, Texas and Franklin County, Wash.

Back in 2000, 5 percent or more of the population spoke English less than very well in 542 counties. This number has since increased to at least 603 counties throughout the U.S.

The 5-percent threshold is similar to the standard specified by the Voting Rights Act in determining jurisdictions required to provide language assistance to voters.

Data shows the number of those speaking English less than very well is growing more rapidly than the total population. The language group jumped 18.3 percent from 2000 to 2010, nearly doubling the overall 9.7 percent U.S. population increase.

On the state level, counts of non-English speakers rose over the decade in all but seven states.

California reported the highest percentage of such residents. One of every five Californians speaks English less than very well, according to U.S. Census Bureau estimates.

Several southern states reported significant increases over the decade. View 2000 and 2010 state totals in the map below:

Powered by Tableau Source: U.S. Census Bureau  View language assessment data for each county