Is the United States of America singular or plural?
Usage notes
During the first few decades after independence authors commonly treated United States as a plural noun, but in contemporary English it is always singular.
Short answer: in contemporary English, both USA and the long form United States of America are treated as singular nouns.
Before 1861 the two words "United States" were generally used as a plural noun: "the United States are a republic." After 1865 the United States became a singular noun. The loose union of states became a single nation. Lincoln's wartime speeches marked this transition.
Already, as a result of Secretary Foster's careful historical research on the subject, the House of Representative's Committee on Revision of the Laws had ruled in 1902 that "the United States" should be treated as singular, not plural.
United States (plural or singular?)
Think of United States as the name of a country like any other. England, China, and Bahrain, for example, are all treated as singular nouns. United States is the same, even though it takes the form of a plural noun.
The United States, or the United States of America in full, takes a singular verb because the term designates a single country rather than a collection of states. The expression these United States appears occasionally in American publications, but this plural form is not recommended in formal writing.
This is because country is a singular noun, and needs the singular form of the verb “have”. The word country is also in the third person singular; in other words, we are referring to either he, she, or it.
The United States is a singular country, as such the correct pronoun, in the United States, is it. Other English-speaking people use plural pronouns when referring to one group composed of many individual entities (in this case, States — they, for instance), which is also acceptable — even in the United States.
Answer and Explanation: The noun 'American' is a proper noun. It refers to a specific person, as in 'The American had a hard time reading the menu in the restaurant in Tokyo.
The Oxford English Dictionary traces singular they back to 1375, where it appears in the medieval romance William and the Werewolf. Except for the old-style language of that poem, its use of singular they to refer to an unnamed person seems very modern. Here's the Middle English version: 'Hastely hiȝed eche . . .
Is all of U.S. plural?
Because “us” is a plural pronoun, it's always appropriate to say “all of us are.” For example, you could say, “All of us are going to attend the Christmas festival at the end of the year.”
The words “moose,” “sheep” and “shrimp” do not have a plural form, but they can be used in singular or plural form as they are. For example: – The moose is/are migrating.

Plurality or multiplicity is the psychological phenomenon in which a body can feature multiple distinct or overlapping consciousnesses, each with their own degree of individuality. This phenomenon can feature in identity disturbance, dissociative identity disorder, and other specified dissociative disorders.
Because sometimes Google ranks different pages for the singular vs plural form of the words. This usually happens when there is different Search Intent behind those keywords, and can sometimes indicate whether one of the phrases has a different meaning than its counterpart.
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country in North America. It consists of 50 states, a federal district, five major unincorporated territories, nine Minor Outlying Islands, and 326 Indian reservations.
US tends to be the more popular way to abbreviate United States. Both of these abbreviations can serve as either adjectives or nouns. However, some style guides prefer United States as the noun form and US as the adjective form.
The noun 1960's is plural only. The plural form of 1960's is also 1960's.
The noun 1970s is plural only. The plural form of 1970s is also 1970s.
Names of decades and centuries (the 1800s, the 1970s, the eighties, the '90s) are generally considered plural but can also be singular. Use plural verbs to show a period of years (e.g., 1970 to '79); use singular verbs to refer to one period of time (e.g., the decade of the '70s).
The noun 1980's is plural only. The plural form of 1980's is also 1980's.