Katherine Alexander Duer Mackay (1878–1930) was an American suffragist, socialite and writer from New York city.

[9] Once, the Trinity Episcopal Sunday School members were invited to Harbor Hill for a picnic where the children inducted her as an "honorary knight".

[2] During her term on the board, she was able to successfully remove corporal punishment from the public schools in Roslyn.

[11] She also enrolled her own children in the public schools in Roslyn because she felt that "it is necessary for the rich as well as the poor to patronize them.

[14] Mackay's involvement in the suffrage movement helped combat the stereotype of suffragists as "frumpy" or "unwomanly".

[16] Mackay encouraged people to become educated about suffrage and organized a series of lectures at the Garden Theater.

[18] Speculation that Mackay left EFS for reasons other than demands on her time included her apparent "dissatisfaction over the management of the campaign to get suffrage bills passed by the Legislature.

[22] Mackay was sued by Catherine Ketcham Blake for the alienation of affections of her husband in 1913 for the sum of $1,000,000.