Internal, first-order administrative boundaries and polygons for the United States (.shp), converted to .geojson (QGIS), and .topojson (http://mapshaper.org/).
reference data here:
http://www.naturalearthdata.com/downloads/110m-cultural-vectors/110m-admin-1-states-provinces/
and repo is here:
https://github.com/nvkelso/natural-earth-vector/tree/master/110m_cultural
datasets/geo-boundaries-us-110m
Internal, first-order administrative boundaries and polygons for the United States in .shp, .geojson, and .topojson.