Why does the New Testament have so many more demons than the Old Testament?

Three identifiable mechanisms produced the explosion -- and none of them is "the New Testament invented demons."

First, the translators changed the vocabulary. When Jewish scholars translated the Hebrew Scriptures into Greek (the Septuagint, 3rd-1st centuries BC), they made a fateful choice at Psalm 96:5. The Hebrew calls pagan gods elilim (אֱלִילִים, "worthless things, nothings"). The Greek translation calls them daimonia (δαιμόνια, "demons"). What the Hebrew dismissed as empty, the Greek declared actively hostile. That single rendering fed directly into Paul's theology:

"What the Gentiles sacrifice, they sacrifice to demons and not to God." -- 1 Corinthians 10:20

Paul isn't inventing a category here. He's reading the Greek Old Testament and treating its interpretive choice as authoritative. The translators did the same thing with other Hebrew terms -- the "goat-demons" (sa'ir, שָׂעִיר) of Isaiah 13:21 became daimonia, and the abstract "destruction" (qeteb, קֶטֶב) of Psalm 91:6 became the "noonday demon." By the time the Septuagint was complete, Greek-speaking Jews had a demon-saturated Scripture.

Second, the literature between the testaments built on those seeds. Books like Tobit introduced named demons, binding rituals, and angelic combat. The Wisdom of Solomon made the first explicit connection between the serpent in Eden and the devil. 1 Enoch expanded Genesis 6 into a full mythology of fallen angels. These weren't canonical Scripture, but they were the cultural furniture Jesus' audience carried into the synagogue.

Third, Jesus adopted the vocabulary but changed everything else. He didn't debate whether demons exist -- he cast them out. But unlike Tobit's exorcism (which required fish-liver smoke, prayer, and an angelic intermediary), Jesus acted with a single word of command. The crowd in Capernaum identified exactly what was different:

"What is this? A new teaching! With authority he commands even the unclean spirits, and they obey him." -- Mark 1:27

The word for "demon" (daimonion, δαιμόνιον) appears only 7 times in the canonical Greek Old Testament. It appears 63 times in the New Testament -- 47 of those in the Gospels alone. The vocabulary didn't change. The power dynamic did.

For the full three-stage trajectory -- translation, expansion, and sovereign reframing -- see the study "Between the Testaments" -- From Silence to Storm.