"Datum" is rarely used in the US, unless you want to sound pretentious. (This coming from someone who cringes every time "who/whom" is used incorrectly.) We use

"Datum" is rarely used in the US, unless you want to sound pretentious. (This coming from someone who cringes every time "who/whom" is used incorrectly.) We use "data" as an uncountable noun.