SR 240 was created during the 1964 state highway renumbering as part of the new sign route system, replacing SSH 11C and the eastern section of SSH 3R. The Richland–Kennewick freeway was renumbered in 1967 after US 12 was extended west to replace portions of US 410. US 12 was then moved onto the newly-completed I-182 in the 1985 and SR 240 was extended east to a junction with the relocated US 395 in Kennewick. The Richland Bypass was also widened from two lanes to five in 1980, at a cost of $1.83 million.