Toner Family, 1875

When I was at the NYPL a few weeks ago, I found the 1875 NYS Census of the Toner family. 

This is important, because it's the first time that I've actually been certain I was seeing young Julia (my great-great-grandmother) as a member of her family. Though I've seen plenty of records connecting my Julia Toner to this Toner family, I had yet to find her listed as a member of this family on a census. Given that she's 8 years old here in 1875, I also find it likely that she is, in fact, the same person as the 2-year-old Judith listed on the 1870 census. The Toner family has a strange relationship with the names Judith and Julia, each of which often pops up where it isn't expected, and disappears from places where it should be. They are sometimes used interchangeably, and sometimes flat-out incorrectly. Here, the family is listed as
Thomas Loughlin, 34, caulker
Eliza Loughlin, 18

Richard Toner, 49, painter
Julia Toner, 46
Mary A. Toner,  21
Louisa Toner, 17
John Toner, 15
Julia Toner, 8

The apparent errors here are Julia Toner, 46, and John Toner, 15. The wife/mother of this family was Mary, not Julia - but I've ceased to be surprised when one of the Toners is incorrectly called Julia. Pretending to be named Julia must have been their favorite hobby - unless this name is a clue to something bigger that I'm just looking right past? The son who would have been 15 in 1875 - indeed, the only son who had survived to 1875 - was named William.

Elizabeth Toner married Thomas Loughlin in 1874. Both here and in 1892, the Loughlins are living with Elizabeth's parent(s). In 1875, they live with both Toners and all of Elizabeth's siblings; in 1892, the Loughlins and their children living with Elizabeth's mother, Mary Tonner.

The Toners have a reliable presence in census records as well as newspapers from 1860 to about 1875, and then everything goes wacky. I can't find anyone but the Loughlins in the 1880 census. In the 1892 NYS Census, the Loughlins are back, this time with Elizabeth's mother Mary Toner living with them - but no mention of any of her other children. I can find Mary Ann Toner married to Thomas Murphy and living with their children, but that's all. Richard is presumably dead. Julia is gone until 1900, and her soon-to-be-husband is single when he's enumerated with his relatives - they didn't marry until the next year. Louisa never again appears in census records that I've seen, but doesn't die until 1918, at which point her death certificate indicated that she had been living uninterrupted in New York City for her entire life. William doesn't appear to show up in 1880 or 1892, but was also apparently a life-long resident of NYC when he died in 1899. Where did they all go?