U.S. TopoJSON

These county, state and country boundaries are extracted from a single TopoJSON file. Counties are stroked in thin gray, states in thin black, and the country in thick black.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

path {
  fill: none;
  stroke: #000;
  stroke-width: .5px;
}

.land-boundary {
  stroke-width: 1px;
}

.county-boundary {
  stroke: #aaa;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js"></script>
<script>

var width = 960,
    height = 500;

var path = d3.geo.path();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

d3.json("/../../data/us.json", function(error, topology) {
  if (error) throw error;

svg.append("path")
      .datum(topojson.feature(topology, topology.objects.land))
      .attr("d", path)
      .attr("class", "land-boundary");

svg.append("path")
      .datum(topojson.mesh(topology, topology.objects.counties, function(a, b) { return a !== b && (a.id / 1000 | 0) === (b.id / 1000 | 0); }))
      .attr("d", path)
      .attr("class", "county-boundary");

svg.append("path")
      .datum(topojson.mesh(topology, topology.objects.states, function(a, b) { return a !== b; }))
      .attr("d", path)
      .attr("class", "state-boundary");
});

</script>

Changed /mbostock/raw/4090846/us.json to a local referenece

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js

https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js