Foreign-born Americans and their descendants have historically been a main driver of population growth, and that role will only increase in the future. The Pew Research Center projects the population will grow to 441 million in 2065, with 88% of the increase linked to future immigrants and their descendants. This measure also reflects the composition of a community, which can offer insight into its levels of diversity.

In 2019-23, 6% of Lancaster County's population was foreign-born, up two percentage points from 2009-13. The percentage of foreign-born people in Lancaster County was slightly lower than Pennsylvania, at 7%, and 8 percentage points lower than the nation, at 14%.

Among neighboring counties, there were smaller foreign-born populations in Lebanon and York (both 4%) and larger foreign-born populations in the City of Lancaster (14%) and the counties of Chester (10%), Berks (9%), Dauphin (9%) and Cumberland (7%). The largest increases in this population from 2009-13 to 2019-23 were in the City of Lancaster and Dauphin County (up 5 and 3 percentage points, respectively).

The multiyear figures are from the Census Bureau's American Community Survey. The bureau combined 5 years of responses to the survey to provide estimates for smaller geographic areas and increase the precision of its estimates. However, because the information came from a survey, the samples responding to the survey were not always large enough to produce reliable results, especially in small geographic areas. CGR has noted on data tables the estimates with relatively large margins of error. Estimates with three asterisks have the largest margins, plus or minus 50% or more of the estimate. Two asterisks mean plus or minus 35%-50%, and one asterisk means plus or minus 20%-35%. For all estimates, the confidence level is 90%, meaning there is 90% probability the true value (if the whole population were surveyed) would be within the margin of error (or confidence interval). The survey provides data on characteristics of the population that used to be collected only during the decennial census. Data for this indicator are released annually in December.