I am looking for a download source which has the highest resolution (greatest detail/accuracy) for all counties in the US. More specifically I run into this problem mainly when dealing with the shorelines. I realize that one can download high resolution shoreline data, overlay the tiger shapefiles for the counties and then clip them but I figured someone might have already done this.
It looks like you are trying to combine data from tiger shapefiles, links to which have been provided by @Boyle300 and @Kurt, with high res shoreline data. My immediate thought for that was to try NOAA (National Oceanographic and Atmospheric Association). Here is their Shoreline Data Explorer: NOAA Shoreline Data Explorer.
This link has metadata about this data source: NOAA Shoreline GIS
From this site, you can download both medium and high resolution data, depending on availability.
Another option, though significantly more time consuming, would be to search out the GIS sites for each county, as they tend to be a central data aggregator, and may have something more specialized regionally. An example of this would be SANGIS for San Diego County.
Good luck with your search!
Here's the 2010 census shapefile home page if you want the most up to data census data. http://www.census.gov/geo/www/tiger/tgrshp2010/tgrshp2010.html
I am unaware of anything with better detail than that. What are you trying to accomplish with the data?
Hope This Helps