I'd like to add that if there are Null values in the column you are counting you may get unexpected or unwanted values.
DCount("*", "SalesRecord")
Result: 1048575 in 0,015625s
DCount("Country", "SalesRecord")
Result: 1048570 in 0,125s
DCount("1", "SalesRecord")
Result: 1048575 in 0s