The actress, who plays Naomi Clark on The CW's teen drama, told Life & Style that the news was a "shocker".
"We found out via Twitter - that wasn't cool at all," McCord admitted.
The show has aired on The CW since 2008 and will end after its fifth series concludes in May. The show's cancellation was confirmed last month, following declining ratings in recent seasons.
The 25-year-old actress added that it is "emotional" and "bittersweet" to say goodbye to the show.
"We've had a great time. All things have to end and new things begin," she said.
However, McCord has admitted that she is unhappy with the ending given to her character Naomi Clark after writers chose to revise it.
"They rewrote the ending and I liked the original, so I filmed my own ending - a surprise for the fans," she confessed.
She insisted that she will give fans a link to the footage directly after the series finale airs in May.
90210 will conclude on The CW at 9pm ET on May 13. The final series is scheduled to air in the UK this summer on E4.