It's not just the KJV, they all do.
New International Version
Everyone who sins breaks the law; in fact, sin is lawlessness.
New Living Translation
Everyone who sins is breaking God’s law, for all sin is contrary to the law of God.
English Standard Version
Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness.
Berean Study Bible
Everyone who practices sin practices lawlessness as well. Indeed, sin is lawlessness.
Berean Literal Bible
Everyone committing sin also commits lawlessness; and sin is lawlessness.
King James Bible
Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
New King James Version
Whoever commits sin also commits lawlessness, and sin is lawlessness.
New American Standard Bible
Everyone who practices sin also practices lawlessness; and sin is lawlessness.
NASB 1995
Everyone who practices sin also practices lawlessness; and sin is lawlessness.
NASB 1977
Everyone who practices sin also practices lawlessness; and sin is lawlessness.
Amplified Bible
Everyone who practices sin also practices lawlessness; and sin is lawlessness [ignoring God’s law by action or neglect or by tolerating wrongdoing—being unrestrained by His commands and His will].
Christian Standard Bible
Everyone who commits sin practices lawlessness; and sin is lawlessness.
Holman Christian Standard Bible
Everyone who commits sin also breaks the law; sin is the breaking of law.
American Standard Version
Every one that doeth sin doeth also lawlessness; and sin is lawlessness.
Aramaic Bible in Plain English
But whoever commits sin commits evil, for sin is entirely evil.
Contemporary English Version
Everyone who sins breaks God's law, because sin is the same as breaking God's law.
Douay-Rheims Bible
Whosoever committeth sin commmitteth also iniquity; and sin is iniquity.
Good News Translation
Whoever sins is guilty of breaking God's law, because sin is a breaking of the law.
International Standard Version
Everyone who keeps living in sin also practices disobedience. In fact, sin is disobedience.
Literal Standard Version
Everyone who is doing sin, he also does lawlessness, and sin is lawlessness,
New American Bible
Everyone who commits sin commits lawlessness, for sin is lawlessness.
NET Bible
Everyone who practices sin also practices lawlessness; indeed, sin is lawlessness.
New Revised Standard Version
Everyone who commits sin is guilty of lawlessness; sin is lawlessness.
New Heart English Bible
Everyone who sins also commits lawlessness. Sin is lawlessness.
Weymouth New Testament
Every one who is guilty of sin is also guilty of violating Law; for sin is the violation of Law.
World English Bible
Everyone who sins also commits lawlessness. Sin is lawlessness.
Young's Literal Translation
Every one who is doing the sin, the lawlessness also he doth do, and the sin is the lawlessness,
lawlessness
ἀνομίαν (anomian)
Noun - Accusative Feminine Singular
Strong's 458: Lawlessness, iniquity, disobedience, sin. From anomos; illegality, i.e. Violation of law or wickedness.