Official tool is here
https://data.hrsa.gov/tools/rural-health?tab=StateCounty
Better tool is here
https://transparentgov.net/json2tree/datahub.io/hrsa/byzipcode.html?backgroundlayerurl=https%3A%2F%2Fgisportal.hrsa.gov%2Fserver%2Frest%2Fservices%2FAnalyzerTool%2FAnalyzerTool%2FMapServer%2F0&layer=Rural+Health+Area&_center_zoom=12&_center_lat=46.587408895265874&_center_long=-94.9460339614999
You can search by zip code, or city name, or state abbreviation
Check Result
OR
Type zip code only then
click 'go' button
https://transparentgov.net/json2tree/datahub.io/hrsa/byzipcode.html?backgroundlayerurl=https%3A%2F%2Fgisportal.hrsa.gov%2Fserver%2Frest%2Fservices%2FAnalyzerTool%2FAnalyzerTool%2FMapServer%2F0&layer=Rural+Health+Area&_center_zoom=9&_center_lat=60.47915594336287&_center_long=-154.6776499999999&search=00005
More layers to look up here
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=123&select_layer=0