Viewer model number 11, multilayer limit on same map server allow you mix all the layers on the same map server.
https://transparentgov.net:3200/googlemaps11/default?layer_id=12&layer=Counties¢er_lat=34.81746059906692¢er_long=-116.64524423347737¢er_zoom=8&url=https%3A%2F%2Fgisportal.hrsa.gov%2Fserver%2Frest%2Fservices%2FAnalyzerTool%2FAnalyzerTool%2FMapServer&overlayType=overlayType_image&panto=0&exportLayerList=show%3A0%2C12&multilayerIDlistString=0%2C12&identifyLayerList=visible%3A0%2C12
https://transparentgov.net/json2tree/esri/server/folder.html?org=https%3A%2F%2Fgisportal.hrsa.gov%2Fserver%2Frest%2Fservices&url=https%3A%2F%2Fgisportal.hrsa.gov%2Fserver%2Frest%2Fservices&select_folder=118&select_layer=12
Official government website is here
https://data.hrsa.gov/tools/rural-health?tab=StateCounty