As both noun and verb, the word regard has numerous meanings and uses in English.
Sometimes it is correctly used in the plural; sometimes not.
For example, in the polite formula Give my regards to your family, regard is correctly rendered in the plural. In this context, “regards” means “affectionate or respectful feelings.”
In the expressions with regard to, in regard of, and in regard to, however, adding s to regard is nonstandard usage. The following examples from the web illustrate the error:
Irving Weighing Options In Regards To Draft
I have a question in regards to joining the Navy.
If the request is not related to a particular product or is in regards to multiple products, select the first option…
With regards to others who posted “early” because of the same issue…
Many speakers and writers do add the s in these contexts, so if you want to do so, you’ll have plenty of company. However, if you are choosy about the company you keep, you may wish to consider what the respected writing guides have to say about “in regards to.”
The Chicago Manual of Style places “in regards to” in its section on “good usage versus common usage”:
in regard to. This is the phrase, not “in regards to.” Try a single-word substitute instead: about, regarding, concerning.
The Oxford English Dictionary lists “in regards to,” but labels it “regional and nonstandard.”
The Columbia Guide to Standard American English (1993) accepts In and with regard to, regarding, and as regards as “Standard,” but firmly declares that with regards to is “Nonstandard.”
Paul Brians at Washington State University has no patience with it either:
Business English is deadly enough without scrambling it. “As regards your downsizing plan…” is acceptable, if stiff. “In regard to” and “with regard to” are also correct. But “in regards to” is nonstandard. You can … convey the same idea with “in respect to” or “with respect to,” or–simplest of all–just plain “regarding.”