Must have died before 1864 when his wife died a widow.

DoB from entry in Civil Deaths, where she was aged 70 in 1864.

Death record in Civil Records shows Bethy (or perhaps Betty) Gray, a widow, aged 70 years, described oddly as a labourer, dying of "Ch bronchitis, 5 years certified, James Gray, "Son of the deceased", from Cullyvenny, Present at Death.

I just got the research for Elizabeth Burk.  Still not found.
That now leaves the years 1916-1920!  she was very old when she died.  It is Yonkers - just north of NYC.  I will send for the next search today (140409).

DoB taken from aged 22 at marriage in 1846.

Gives her age as 22 on marriage = DoB 1824.
DoB = Mac Pres Ch register.

Could this be Mary Gray Dickson's death?  She possibly died when Margaret was born which doesn't much but you could get it at Derry.
Name: Mary Dickson
Registration District: Coleraine
Event Type: DEATHS
Registration Quarter and Year: 1865
Estimated Birth Year: 1825
Age (at Death): 40
Mother's Maiden Name:
Film Number: 101582
Volume Number: 11
Page Number: 279
Digital Folder Number: 4200214
Image Number: 00355
Collection: Ireland, Civil Registration Indexes, 1845-1958

Full age on marriage certificate.

However, if he is the James who was from Camus, he was not baptised until 1830. 

Death Register entry from General Registry Office, Dublin shows: James Gray, died 21st December 1898 at Cullyvenney, married, 70 years, labourer, of pneumonia after 8 days certified, Present at Death was James Gray, son, of Cullyvenney, who made his mark.  A death notice appeared in the Coleraine Chronicle on 24th December 1898, giving his date of death as 22nd December!  No other details were given in the death notice other than that he was from Cullyvenney.

I need her death cert  - aft 1910 Census.

BB Summary:
She died after 1912
Need a search for her death cert in Yonkers.
sent for 3 yr search Nov 6, 2008
12/23/08 - No death record found for Elizabeth Burk - 1910, 1911, 1912
sent for 3 yr search Feb 18, 2009-- 1913, 1914, 1915
4/13/09 - No death record found for Elizabeth Gray Burk - 1913, 1914, 1915
4/14/09 -sent for a 3 yr search -- 1916, 1917, 1918
6/06/09 - No death record found for Elizabeth Burk
11/11/09 - No death record found for Elizabeth Burk in years 1919, 1920 or 1921

Gives his age as 40 in the first US 1870 census, 38 in the second US 1870 census and 48 in the 1880 census.

His DoB is confirmed by his death certificate, where he is given as 57 in 1892.

However, if he is the Samuel who was from Camus, he was baptised in 1832!

BB: I also found what may be Samuel Gray's death record.
I put it in the shoebox.  It says born 1835 and died
Jan 1, 1892, NYC.

The death certificate was fairly conclusive.  He suffered a fall (hard to read but it may have been from a house) on 30th December 1891 and died of "cranial haemmhorrage" on 1st January 1892 in Bellevue Hospital.  He was buried at New York Bay on Jan 3rd 1892.  His occupation was given as a driver and he was a widower, he was born in Ireland and had been in the States for 30 years and his parents were both born in Ireland.  His father was James Gray and his mother was Elizabeth (no surname given).  He was 57.

Source: aged 33 in 1870 census.

However, if he is the William who was from Camus, he was baptised in 1836!

Disappears between the 1880 and the 1900 census (there is no 1890 census), when his wife is a widow.

BB sent for and received a death record for a William Gray, died 29th Jan 1893 but he turned out to be a Catholic bachelor, born in the US, father called Richard.

The same source who gives William as married to a Jane Carson give his death as 1882.

From A.com via BB:
1890 City Directory - NYC - [Census substitute]
Gray Margaret, wid. William, h 204 Eighth av.
This shows William was dead by 1890.

BB received death cert from NY Deaths for a William Gray who died on 24 Feb 1881 @ 4:05pm, aged 48 years, which fits roughly with his DoB of 1837.  It gives his birthplace and that of his father as Ireland but it says he was in the States for 33 years and in fact he was only there for 21 years in 1881.  Also, he died in Mulverry street rather than West 13th Street, which is where he was living in 1880.  So, this is probably not him.  He died of Phthisis, Brights Disease, Mitral Regurgitation and Asthenia.

BB: I ordered 1881, 1883, 1884, 1885, 1886 to be searched for William Gray on 9/21/08  #2203119201.  Received letter:  NOT FOUND - included a death cert, however, for a William Gray, age 48, widower who died in Charity Hospital in 1881.  Even if him there is no indication of parents and he was 15 years old when he emigrated. (33 yre in nyc).  I ordered 1887, 1888, 1889 and 1890 to be searched for William Gray (died in Manhattan) on 1/28.09  #3318843874.  Mail just arrived- and they did NOT find William Gray 1887-1890.  I am now thinking that if he did die in 1882 as it said on familysearch.org then it was not in Manhattan but possibly another borough of NYC.