According to researcher Cora R. Swift, Charles married Susannah Fass on June 2, 1836, in Lancaster County, Pennsylvania.

Susannah, born February 15, 1815, in Pennsylvania, was reportedly the daughter of Samuel and Mary (Rollins) Fass.  This surname is also found as Foss; on marriage documents for Susannah's daughters, Susan and Mary, it was spelled Fass and Fas.

Of all the children of Thomas Callihan, two sons consistently used the spelling Callahan: Charles and Evan.  The spelling Callihan was used in the papers filed when Thomas' estate was settled and Charles' tombstone was inscribed with Callihan.  Another exception is the possible 1840 census listing, displayed below.

From the marriage documents of Charles and Susannah's daughters, Susan and Mary, Calahan and Callahan were the maiden names recorded.  For those of Charles and Susannah's children buried at Majorville Cemetery, both Callahan and Callihan are the surnames found on their tombstones.

Another fact sets Charles apart from those of his siblings for whom there is documentation: Charles and his family were in Hancock County, Illinois, as of June 1, 1850, but they returned to Pennsylvania shortly thereafter.  If location can be inferred based on the families named both before and after Charles and Susannah in the 1850 Federal Census, they were living amidst families known to be longtime residents in the area of Fountain Green and Hancock Townships.

The obituary of Charles and Susannah's second eldest daughter, Elizabeth, reported the family initially traveled from Pennsylvania to Illinois by "steamship down the Ohio river and up the Mississippi to Warsaw where they were met by Mr. Callihan's brother, a settler at Webster, and conveyed across the prairie of Hancock county in an open wagon", and that the family remained in Hancock County for only one year, then returned to Pennsylvania.  The marker for David Callahan at Majorville, believed to have been Charles' and Susannah's son, indicates he was born November 26, 1850, and census records indicate he was born in Pennsylvania.  The base date for the 1850 Federal Census was June 1, 1850, which means - if everything is accurate - Susannah made that long trip back to Pennsylvania while she was pregnant with David.

The family remained in Pennsylvania for twenty-odd years.  Daughter Susannah, born in 1858, reported she was born in Lancaster County; this location was also mentioned in her obituary. Daughter Mary, born in late 1860, said she was born in Union County, which is where the family was counted in the 1860 Federal Census.  In 1870 they were living in Northumberland County. (Formation of counties does not come in to play in this scenario.  Lancaster County was formed in 1729, Northumberland County in 1772, and Union County in 1813.)

It's interesting that in the obituary for son Jacob, it was stated that Jacob and his wife had come to Hancock County in 1872, with no mention of the fact it was a return trip for Jacob.  The obituary for Jacob's wife also said they came to Hancock County in 1872.  The obituary for daughter Elizabeth reported that the entire family returned to Hancock County in 1871.

Susannah died July 19, 1886; Charles died February 6, 1901.  They were both buried at Majorville Cemetery.

Charles and Susannah were the parents of eleven children, according to the obituaries of their son, Jacob, and daughter, Susan:

i.	Female child, recorded as between 5 and 9 years of age in the 1840 census.  This daughter apparently did not survive until 1850.
ii.	Female child, recorded as between 5 and 9 years of age in the 1840 census.  This daughter apparently did not survive until 1850.
iii.	Anna Callihan, born February 10, 1837, in Pennsylvania, died November 6, 1901 - the same year as her father, in Hancock County.  (The year of birth on Anna's tombstone was interpreted in the 1960s as 1887.)
iv.	Elizabeth A. Callahan, born September 15, 1839, in Lancaster County, Pennsylvania.  Over the course of her life she lived in Pennsylvania, Illinois, Pennsylvania, Kansas, Arkansas, and then again in Illinois.  She died September 28, 1913, at Carthage, Hancock County, and was buried at Majorville Cemetery.
v.	Fianna Callahan, born about 1841 in Pennsylvania.  Another marker at Majorville has been previously read as Fianna Callahan, Dau. of G. and S. Callahan, died June 7, 1885, age 13Y. 7M. 3D.  A daughter named Fianna (or some variation of that spelling) was counted in her parents' home from 1850 through 1880.  There is no record of this Fianna Callahan or Callihan marrying in the state of Illinois, although she could easily have married in Iowa or Missouri, like many Hancock County residents.  However, if that tombstone actually reads Dau. of C. and S. Callahan, died June 7, 1885, age 43Y. 7M. 3D., which calculates to a birth date of November 4, 1841, this would dovetail perfectly with what we know about this daughter.  We have not found a married couple named G. and S. Callahan.
vi.	Jacob Callihan, born March 14, 1844, in either Northumberland County or Lancaster County, Pennsylvania.  He died April 9, 1925, at his home in or near Fountain Green, Hancock County, Illinois, and was buried at Moss Ridge Cemetery, Carthage, also in Hancock County.  He was survived only by sisters Susan and Mary.
vii.	David Callahan was born November 26, 1850, in Pennsylvania and died October 4, 1871. Presumed to be buried at Majorville Cemetery, but given the family's travels, another possibility is that he died elsewhere (around the time the family returned to Hancock County) and the marker was commemorative.
viii.	Susannah Callahan, usually found as Susan or Susie, born November 9, 1858, in Lancaster County, Pennsylvania.  She died December 25, 1928, in Keokuk, Lee County, Iowa, burial at Oakland Cemetery in Keokuk.  Her maiden name is found as Callahan or Calahan.
ix.	Mary M. Callahan, born about 1860 in Union County, Pennsylvania.  She died November 5, 1946, in Carthage, Hancock County, Illinois.  She was the last surviving sibling.  Mary's maiden name was spelled Callahan on all documents found to date.
x. xi.	Two male children: Susannah Callahan Walsmith's obituary stated she had been preceded in death by four brothers and five sisters.

Household of Thomas Callihan
Males 0 thru 4 - 2        (Evan 1828, Undetermined male)
Males 5 thru 9 - 1        (Jacob 1820, William 1821-22)
Males 10 thru 14 - 1    (Charles 1818)
Males 15 thru 19 - 1    (Undetermined male)
Males 20 thru 29 - 1    (John 1808)
Males 50 thru 59 - 1    (Thomas Sr)
Females 5 thru 9 - 1    (Elizabeth 1823)
Females 40 thru 49 - 1    (Margaret)
Total - 9

Charles Callahan, 32, male, blacksmith, value of real estate 50, born PA
Susannah, 36, female, born PA
Ann, 14, female, born PA, attended school within the year
Elizabeth, 10, female, born PA, attended school within the year
Phiana, 8, female, born PA, attended school within the year
Jacob, 6, male, born PA, attended school within the year

C Callahan, 42, male, blacksmith, value of real estate 1000, value of personal estate 100, born PA
S Callahan, 45, female, born PA
A Callahan, 23, female, born PA
S A Callahan, 21, female, born PA
Fianna Callahan, 19, female, born PA
Jacob Callahan, 14, male, laborer, born PA, attended school within the year
David Callahan, 7, male, born PA
Susan Callahan, 4, female, born PA
Wm T Kleckner, 2, male, born PA

Callahan, Charles, 52, male, white, farmer, value of real estate 42?? [illegible], born PA, male citizen of the U.S. aged 21 or more
Susannah, 55, female, white, "kaping" house, born PA
Annie, 35, female, white, at home, born PA
Phiana, 26, female, white, at home, born PA
David, 16, white, male, farm laborer, born PA, attended school within the year
Susanah, 12, female, white, at home, born PA, attended school within the year
Mary, 10, female, white, at home born PA, attended school within the year
Heckner, William, 10, male, white, at home, born PA, attended school within the year
Morgan, Charles, 1, male, white, at home born PA

Callahan, Charles, white, male, 62, married, farmer, born PA, both parents born PA
Susan, white, female, 65, wife, married, keeping house, born PA, both parents born PA
Anna, white, female, 39, daughter, single, at home, born PA, both parents born PA
Fiana, white, female, 34, daughter, single, at home, born PA, both parents born PA
Sue, white, female, 23, daughter, single, at home, born PA, both parents born PA
Mary M, white, female, 21, daughter, single, at home, born PA, both parents born PA
William J, white, male, 20, gd son, single, works on farm, born PA, both parents born PA
Chas H, white, male, 11, gd son, single, at school, attended school within the year, born PA, both parents born PA
Thos F, white, male, 5, gd son, single, born IL, father born IL, mother born PA
Monroe, white, male, 2, gd son, single, born IL, father born IL, mother born PA

Callahan, Charles, head white, male, July 1818, 81, widower, born PA, father born "Scoltand", mother born PA, retired farmer, months not employed - 12, could read, write and speak English, owned his home free of mortgage

Anna, daughter, white, female, Feb 1837, 63, single, born PA, both parents born PA, could read, write and speak English