Peter must have lost his father relatively early in life because he was listed on the 1905 New York Census as 23 years old, living on E. 138th Street in the Bronx with his widowed mother, age 38, and a 21-year-old lodger, Miss Aida Brisdale (or "Bisdale"), a typist/secretary. He was working as a Book-keeper in a Dry Goods store.
The 1910 US Census reported Peter J. Masterson, 29, still living with his widowed mother, 47, but now it was just the two of them living on E. 2nd Street in Brooklyn (Kings Co.), where Peter was employed as a New York City Police Officer. Apparently, however, Peter Jr. had continued to see Miss Aida Brisdale because the January 1, 1920 US Census recorded them as a married couple now living on 17th Avenue in Brooklyn, still with his widowed mother. Peter was now a Police Lieutenant at 38 years old; his wife, 37 years old had stopped working and his mother was 57 years old. No children were reported in the home and the Census no longer asked how long couples had been married. 
Alas, Aida T. (Brisdale) Masterson passed away in Brooklyn, New York, on August 11, 1928. She was 45 years old. Her NYC death record stated that she was born January 2, 1883 in New York; her parents were Joseph Brisdale and Ellen Murphy, both born in the USA. She was interred at St. John's Cemetery in Brooklyn, Kings, New York, USA. 
Peter J. Masterson married for a 2nd time between 1928 and 1930 to Jane G. (Unknown), b: 1897 in New York, of Irish parents. On the June 1930 US Census, Jane G. (Unknown) Masterson, b: 1897 in Manhattan, New York, 33 years old, was reported as married to 48-year-old widower, Peter J. Masterson and living with him and his 69-year-old mother: widow Sarah J. Masterson, in Brooklyn (Districts 1751-1953), Kings, New York, United States. No children were listed in the household. Peter J. Masterson's occupation was: Police Captain for New York City. Both of Jane G. Masterson's parents were said to have been immigrants from Ireland. Peter's maternal grandparents were from Ulster, Ireland and Scotland.
Ten years later, on the 1940 US Census, the last publicly available, the Masterson household was comprised of the same 3 individuals. Jane G. (Unknown) Masterson was 43 years old; her husband, Peter J. Masterson was 58 and his mother, Sarah J. Masterson, was said to be 79 years old. They still lived in Brooklyn, Kings County, New York, USA, where Peter J Masterson was now an "Immigration Inspector" for the NYPD. The family owned their home, where they already lived in 1930 and 1935, valued at $8,500.
On January 15, 1944, Peter's widowed mother, Sarah J. Masterson, nee Davis, passed away. Her NYC death notice stated she had lived at 1544 E. 28th Street in Brooklyn, her son's address. Her father, John W. Davis, had been immigrated from Ulster, Ireland, and her mother, Isabella Jarrett, was born in Scotland. Her deceased husband had been Peter Masterson. She was buried beside him at St. John's Cemetery, New York, NY, USA.
It is not known when Peter J. Masterson Jr. passed away. As he was born in 1881, he would have reached 65 in 1946 and should have retired at about that time. It's assumed he died after 1946.
Have you taken a DNA test? If so, login to add it. If not, see our friends at Ancestry DNA.