I have five shapefiles of bordering counties in California that I am trying to combine into one large shapefile and maintain the original borders of the counties. I then want to plot points such as this so the map only needs to be a simple map of county boundaries. Is there a way to do this in R or will I have to use something like ArcGIS?

There is extensive documentation about merging within a shapefile such as here where both shapefiles have the same coordinates. But no documentation on shapefiles that only partially share coordinates.