Where can I get hourly ambient temperature for each county in United States?
You can get this from the Integrated Surface Dataset (ISD).

First get a list of all weather stations from ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd-history.txt:



stations = pandas.read_fwf("ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd-history.txt", 
                           skiprows=20, parse_dates=["BEGIN", "END"],
                           skip_blank_lines=True,
                           dtype={"WBAN": "O"})


Then select the ones in the USA:



stations_us = stations[stations["CTRY"]=="US"]


That give us 7326 stations.  Although the state of each station is described, the county is not.  To get the county you will need to combine the lat/lon for each station with a county database.  That is a bit beyond the scope of Earth Science SE, but maybe you can get help at GIS SE.  The station ID is a combination of two fields:



ids = stations_us["USAF"] + stations_us["WBAN"]


We can then download the measurements for a particular year from AWS S3:



meas = pandas.read_csv(f"s3://noaa-global-hourly-pds/2020/{ids.iloc[200]:s}.csv", parse_dates=["DATE"])


And extract temperatures:



temps = meas.TMP.str.extract(r"([+-]\d{4}),([012345679ACIMPRU])")[0].astype("f4")/10


Let's get the valid ones (there's a 9999 fill value) and plot:



valid = temps&lt;999
meas[valid].set_index(meas.DATE[valid])["temps"].plot()




Enjoy!

For a description of the fields, see the ISD Format Document at https://www.ncei.noaa.gov/data/global-hourly/doc/isd-format-document.pdf .