Similar to the State database table, this will retrieve all of the county data. It accepts a geometry parameter to decide if it will return the geometry of each county:

@app.route('/nba/api/v0.1/county', methods=['GET'])
def get_counties():
  counties = session.query(County).all()
  geoms = {county.id:smapping(to_shape(county.geom)) for county in counties}
  if 'geometry' in request.args.keys():
      data = [{"type": "Feature", 
      "properties":{"name":county.name, "state":county.state.name}, 
      "geometry":{"type":"MultiPolygon", 
  "coordinates":[shapely.geometry.geo.mapping(to_shape(state.geom)["coordinates"]]},
       } for county in counties]
  else:
      data = [{"type": "Feature", 
      "properties":{"name":county.name, "state":county.state.name}, 
      "geometry":{"type":"MultiPolygon", 
  "coordinates":["Truncated"]},
       } for county in counties]
  return jsonify({"type": "FeatureCollection","features":data})