The following study is meant as just that, a study into this family and should NOT be considered a legal document.
Sources were Census records
Berrien County marriage data.
Death certificates
Newspaper articles

Lewis Monty was the son of John Monty and Sarah (Clark) Monty. John died in Clinton Co.,  in March of 1861 at the age of 87 yrs and wife Sarah preceded him in death in Feb 1858
at the age of 65 years. They were laid to rest in Ingraham Cemetery, Ingraham, Clinton County, New York.  For those studying this family see Ingraham Cemetery for more family members.
see History of the "Town of Chazy, Clinton Co., New York" by Nell Sullivan & David Martin 1970.
Lewis was born in Chazy, Clinton Co., New York 15 April 1815 . At times the census taker took poetic license and spelled the name Monte, Montey, and Manty... but that part of the
fun of genealogy is figuring and deciphering some of the old documents.  They lived mainly in the Chazy, Beekmantown and Plattsburg, areas in Clinton County, New York.  

Arrival to Berrien County, Michigan. In an article celebrating  Marie and her husband Freeman Bury celebrating their 60th wedding anniversary in 1946 and she stating that 
her family arrived in the county when she was 6 years old. That would make the date 1873.

Lewis Monty wed Harriet Sears in about 1838 and according to the 1900 census, Harriet states that she had 11 children with 9 surviving as of 1900.
I have accounted for 10 of them, the 11th child may have been born and died between the census taking. 

Lewis enlisted in the Civil War in 1862 into Company H 118th New York Infantry. as a private. Lewis would be affected by wounds received off and on for the rest of his life.
He applied for invalid pension in 1877 in Michigan and then Harriet Applied for it 12 Jan 1911 after his death.

Delia Montey - 1840
She first married  Levi Prindle (1832 to 1 March 1880) in about 1863 in Clinton Co., NY  then wed Byron Johnson on 2 April 1884 in Belroit, Rock Co., Wisconsin. 
It is believed she died after 1920 in Cook Co., IL (need evidence of this)

Melissa Monty  1844 no further references for her.

Leroy Monty  1846  shows as Leban Leroy Monty on Civil War record served, as did his father Lewis, in Company H 118th Infantry New York.  
He died a little before 1900 in the state of Washington, USA.

Myron Monty about 1850  he appears in the 1860 census and again in the US Garrison in Plattsburg, Clinton Co. New York along with is brother Leroy. but no trace of him after that.

Martha (Lillian A) Monty  born March of 1854 and family tree shows she died 21 Mar 1936 in Nooksack, Whatcom, Washington.  (Need evidence of this)

George B. Monty 1857 Actually born September 1856. He lived several years in Berrien County and then (with enticements that were being offered by Washington State) - Historical note
He wed Eunice Bell Rank on the 23 May 1889. They had one child George  Rank Montey.

Francis H. Monty 1860 shown as a male on an early census but later corrected in later census to show female.  Wed Clarance Sales in Berrien Co., MI on 23 Oct 1882. 

Sarah "Sallie" L. Monty  9/27/1862  and died 31 December 1925. She had wed Daniel Hibbard in 1882 and they lived out their life in Berrien County. Stated on her death certificate is
her mothers name was Harriet Sears. This is the second place I found this comment. The first was in History of the "Town of Chazy, Clinton Co., New York" by Nell Sullivan & David Martin 1970.
This could be part of the reason why the confusion exists and we see her maiden name as LeFane or Lafar etc... Perhaps, since she was approximately 23 years of age, might there have been
a brief marriage before this. And a third proof is that her daughter Lillie A (Monty) Hayward w/o Rev. Samuel P. Hayward states that her mother's maiden name was Sears. 

Marie Elizabeth "Libbie" Monty 7/7/1866 and died 29 Nov 1946 She wed Freeman Bury this county 16 June 1866. His dates are 15 Oct 1861 to 22 Apr 1958. Both
are buried in Crystal Springs Cemetery., Benton Harbor, MI.

There were two Lewis Monty's in Clinton County as the same time in the 1850's etc. However the other Lewis Monty  about 1804 and his wife was Jane.
This is where the confusion comes in with William and Hiram Monty. I believe they may have been cousins, but were not the children of Lewis & Harriet. 

Civil War – From the New York Rosters.

MONTY , LEROY.—Age , 18 years. Enlisted, Augus t 4, 1862, at Plattsburgh, to serve three years; mustered i n as private, Co. H , Augus t 30, 1862; discharged for disability,
January 5, 1863, at U . S. Hospital, place not stated. ONE HUNDRE D AND EIGHTEENT H INFANTRY.

MONTY, LOUIS.—Age, 42 years. Enlisted, August 2, 1862, at Plattsburgh, to serve three years; mustered in as private, Co. H, August 30, 1862; discharged for disability,
no date, at U. S. Hospital, place not stated, as Lewis Montey.