Micki - Based on what information I have available to check - Census, BDMs etc. - I have arrived at the following conclusions regarding Maria Loveland. I must say that I am not totally convinced but it is all I can find at the moment.
The first thing I should mention is that there is a Maria Loveland at Shalford, Surrey in the 1841 Census. It is recorded that she was born in Surrey and that she was age 15-19. Unfortunately she is not with parents and I can find nothing to suggest who her parents may have been.
Based on what I have been able to find:-
Robert Loveland married Maria Sims by Banns 24th March 1828 at Saint Pancras, Middlesex
Maria daughter of Robert Loveland, coachman, and Maria was baptised 4th January 1830 at Saint Pancras, Middlesex (born 13th December 1829)
In 1841 Robert and Maria and their daughter were living at Bushey, Hertfordshire where Robert was employed as an agricultural labourer. Robert was age 35, Maria, 40 and daughter Maria age 12. It is also noted that none of the family were born in Hertfordshire.
In 1851 Robert and Maria were living at 10 North Row, Park Lane, St George Hanover Square, Westminster where Robert was again employed as a coachman.
Robert was age 46 and born at Sydenham, Kent and Maria was age 48 and born at Bury St Edmonds, Suffolk.
What concerns me about this is that their daughter Maria was born in December 1829 and so would not have been quite 15 if it were she who married William Baragwanath in 1844.
I believe it was still legal at that time for a girl to marry at 14 but I would think highly unusual.
As you have already mentioned the marriage took place 18th August 1844 at which time Maria said she was age 19. That is where the Maria at Surrey becomes of some interest.
W Baragwanath can be found as head of household in the 1855 Illinois State Census and it appears there are more adults than just he and Maria in the same dwelling.
I have now finally found the family in each Census from 1860 to 1900 and there is some interesting reading.
In 1860 William stated his age as 45 which would have been about four years older than he actually was.
More importantly is that Maria stated she was 42!
which indicated she was born about 1818!
In 1870 we find things probably a little closer to the truth with William then age 51 and Maria 45.
Once again we have Maria's birth at around 1825 (just as with the marriage record) but other information is suggesting this may not be correct.
But in 1880 things change! William is now 60 which closely reflects his true age. But Maria is now 50
which bring her birthdage forward to match the birth record of the daughter of Robert and Maria.
And then in 1900 we find Maria as a widow living still living in Chicago with daughter Jenny.
And this time Maria states she was born in December 1828
The only other thing I have been able to find for Maria is her Death Certificate.
And that tells us that she died at about 11.55am 8th December 1908.
More importantly it tells us that her age was 79 years 11 months 26 days
Using the Tombstone Birthday calculator to calculate the Birthdate using the death date and age above give us:-
8th December 1908 - Date of death
79 yrs 11 mths 26 days - age12th December 1928 - Date of Birth
If we now take another look at the Baptismal record for Maria Loveland:-
4th January 1830 - Date of Baptism13th December 1829 - Date of Birth
From this I have to conclude that the wife of William Baragwanath was Maria daughter of Robert and Maria (nee Sims) Loveland.
Robert Loveland and Maria Sims married in March 1828 so it is possible that the birthdate recorded on the baptismal certificate of their daughter might be incorrect and should possible read 1828.
The alternative is that Maria's birthdate as supplied later in life may have been incorrect.
But there does seem little doubt now that Maria married when she was not quite 16.
And now I think it is your turn.
I notice at the 1900 Census that Maria stated she was the mother of 14 children of whom 5 were then still alive.
Could you please supply me with what details you know of these children?