Which U.S. stock index was most associated with the 1987 Black Monday crash?

The Dow Jones Industrial Average was the U.S. stock index most associated with the 1987 Black Monday crash.

On October 19, 1987, the Dow recorded its largest one-day percentage decline, falling 22.6%. The plunge occurred amid international market turmoil, concerns about overvaluation, rising interest rates, and the growing use of computerized trading strategies.

The Dow is a price-weighted index of major U.S. companies, so its point and percentage movements are not identical to those of broader market measures. The S&P 500 also suffered a severe fall that day, but the Dow’s record percentage drop made it the best-known symbol of the event.

Black Monday did not develop into a prolonged depression like the 1929 crash. Markets stabilized, and reforms later addressed trading halts and automated selling pressures.