Trivia is a relatively recent word - its first recorded usage, according to the OED, is 1902. It is more likely these days to be followed by a singular verb than a plural one, but etymologically, trivia is the plural of the Latin word trivium (just as bacteria is the plural of bacterium).
In the medieval era university education was based on seven liberal arts and the first three - grammar, rhetoric and logic - were called the trivium. These were studied first in order to give students a sound foundation to continue with the quadrivium, namely arithmetic, geometry, music and astronomy, and thus achieve a fully rounded education. The contrast between the three earlier subjects, considered less important, and the later four, gave us the adjective trivial (first attested with the meaning "unimportant" in the early 17th century).