Mary Lockwood (died 8 September 1864) was a resident of New York City during the 1860s. The sister of Madame Grindel, she met NYPD detective Francis Maguire as he investigated Grindel's murder in 1864, and the two eventually became engaged to marry. Meanwhile, Lockwood used her sister's ledger to blackmail all the men who had paid her sister for secretive abortions, resulting in her makign several enemies. However, she was murdered in Central Park's Sheep Meadow on election day of 1864.