I am assuming J A Huggans is the brother of Davidson base on locale and age.
Some of these census records are disturbing since Mary is either born in OH or PA.
We probably have:
Alex w/ wife Mary born OH
J A w/ wife Mary born PA

CENSUS: 1880 Alexander Huggans
ED 118, Sullivant, Ford Co, IL Page 11
Name Sex Rel Age Mar BPlace Self Fathr Mothr Occupation
Alexander M Head 25 M OH, Scot, Scot Farmer
Mary F Wife 24 M OH, Wales, Wales
Elizabeth F Daug 2 S IL, OH, OH
Wallace? M Son 4/12 S IL, OH, OH

CENSUS: 1900 J A Huggans
Ed 114, Reading twp, Livingston, IL Sh 5A
Name Rel Sex MM Year Age Mar Yrs Place Self Fathr Mothr ImgrYr Occp
J A Head M Oct 1855 44 M 25 OH, Scot, Scot Engineer?
M A Wife F Nov 1855 44 M 25 PA, Wales, Wales
Nan Daug F Oct 1877 22 S IL, OH, PA Book keeper
Wallace Son M Feb 1880 20 S IL, OH, PA Fireman
Ida Daug F Aug 1882 17 S IL, OH, PA
Charles Son M Sep 1884 15 S NE, OH, PA Salesmans
Don Son M Feb 1886 14 S NE, OH, PA At school

CENSUS: 1910 J.A. HUGGANS
April 22: Streator City, part of Ward 5, Bruce Twp, LaSalle, Illinois.
They lived on North Mason Street.
J.A., head, 54 md 1, b. OH, Scotch EngliP, Scot, Scotch; PLUMBER, Shop--, Employee, owns home, Free of m.; Speaks English; can read & write.
MARY, wife, 54 md 1; 4 kids, 3 liv; b. PA; Wales, spk Welsh; Wales -Welsh; English; can r\w
DON L, son, 23, S NE, Ohio, PA; PLUMBER, HOUSE; Speaks Eng; can r\w
CORA M., sister, 39 S; IL; Father b Wales, speaks Welsh; Mother b Wales, Welsh; Speaks English; TEACHER, PUBLIC SCHOOL; can read/write.
LOLLY, sister, 37 S; Illinois, Father b Wales, speaks Welsh; Mother b. Wales -Welsh; Speaks English; can read & write
(?SISTERS? OF J.A. HUGGANS? born in 1871 and 1873??
Not mentioned in James/Agnes 1880. Perhaps the ?two sisters? were COUSINS? )

CENSUS: 1920 J A Huggans
Ward 5, Streator, LKaSalle, IL T625-525, ED 92, Sh 2A
Name Rel Sex Age Mar ImgrYr Birth Father Mother Occp
JA Head M 64 M OH, Scot, Scot Prop, Plumbing Sch
Mary A Wife F 64 M PA, Wales, Wales

CENSUS: 1930 Apr 16: SIDNEY LAHMAN
Streator Ward 5, LaSalle, Illinois, Eleventh St.
SIDNEY LAHMAN Head 49, md at 29. house $3,500, IL IL, VA
MARY LAHMAN wife 52, md at 30 IL, OHIO, PA.
JAMES HUGGANS father-in-law, WIDOWED, age 74, Ohio, Scotland, Scotland, occupation-"NONE".

• Married: 15 DEC 1875 in , LaSalle, IL ⁷

1. Elizabeth HUGGANS b: OCT 1877 in IL
2. Walter HUGGANS b: FEB 1880 in IL
3. Ida M HUGGANS b: 3 SEP 1882 in IL
4. Charles HUGGANS b: SEP 1884 in NE
5. Don Lewis HUGGANS b: FEB 1886 in NE

1. Title: Marker in Cemetery listed
   Abbrev: Marker in Cemetery listed
2. Repository:
   Name: LaSalle Co. Genealogy Guild Library
   Note:
   Very helpful volunteers. Oct 2004
   
   Title: Cemetery Index, LaSalle Co
   Abbrev: Cemetery Index, LaSalle Co
   Page: 37
   Note: J A Huggans family, row 5
3. Title: Minson, Carol (Huggans)
   Abbrev: Minson, Carol (Huggans)
   Note:
   Research file on James A Huggans
   Date: 12 MAR 2007
4. Title: Scherer, Lois Huggans - letters, 1974
   Abbrev: Scherer, Lois Huggans - letters, 1974
   Note:
   Several letters to Margaret Luft in the 1970's
   Note: From Jenkins - Lewis decendent chart created by Margaret Luft from several sources
5. Title: Marker in Cemetery listed with photo
   Abbrev: Marker in Cemetery listed with photo
   Quality: 3
6. Title: US Census - 1870
   Abbrev: US Census - 1870
   Note: Jas Huggins (sic) - Bruce, LaSalle, IL
7. Repository:
   Name: LaSalle Co. Genealogy Guild Library
   Note:
   Very helpful volunteers. Oct 2004
   
   Title: Marriage index, LaSalle Co, IL
   Abbrev: Marriage index, LaSalle Co, IL