Although that date is all over the Internet, I don't believe it and some detailed timelines for individual companies suggest a few years later. [1] [ADDED: As the sibling notes, I'm sure at least cheap slide rules were available perhaps even today. But that date is plausible for "in the US."]
They were killed off pretty quickly though. When I started college in fall on 1975 I got a TI scientific calculator which was somewhere around $100-$200. (It was required.) Prices were in sharp decline. A five function TI calculator was about the same price the year before. A year or two later an older HP model (which were higher-end calculators) was also about the same amount.
Calculators were fairly expensive at first but remember that slide rules weren't useful for adding and for a lot of calculations anyway. [They're not precise enough for everything.] So once engineers, in particular, switched to calculators, there wasn't much of a market for slide rules.
They were killed off pretty quickly though. When I started college in fall on 1975 I got a TI scientific calculator which was somewhere around $100-$200. (It was required.) Prices were in sharp decline. A five function TI calculator was about the same price the year before. A year or two later an older HP model (which were higher-end calculators) was also about the same amount.
Calculators were fairly expensive at first but remember that slide rules weren't useful for adding and for a lot of calculations anyway. [They're not precise enough for everything.] So once engineers, in particular, switched to calculators, there wasn't much of a market for slide rules.
[1] http://www.sliderulemuseum.com/SR_Dates.htm