This function is deprecated as of choroplethr version 3.0.0. Please use ?county_choropleth with the county_zoom parameter set instead. The last version of choroplethr in which this function worked was version 2.1.1, which can be downloaded from CRAN here: http://cran.r-project.org/web/packages/choroplethr/index.html
county_zoom_choropleth(...)
All arguments are ignored.