The dates for this letter make it most likely to be between two of the children of John JACKSON & Elizabeth McCULLAGH. At the end of the letter, the child-like repeating of "adieu" in large script makes it likely to be the work of thethen fourteen year old David JACKSON. This would be the same David JACKSON who would go on to marry Eliza OLIVER and have ten children including Sir Thomas JACKSON.
The address of Ballybay raises more questions than it answers (at least at this moment).
The transcription is thanks to Wendy JACK while the footnotes (and any errors they may reflect) are mine. Sharon Oddie Brown, November 18, 2004
Updated January 31, 2006

Margaretta Jackson,
Urker Lodge.

Ballibay March 5th 1828

Dear Margaretta [1] ,

I am glad of this oppertunity of writing to you to let you now that I was very sick on Satturday and that I had to go to Bed about 12 oclock and was not able to attend the market  I was up on sunday But could not go to meeting there was a great pain in my head and the doctor said that I am very Bilious. I had a great cold ever since, But am getting better.

The shirt which you sent me is about an inch too short in the sleeve and I would like it a little fuller in the neck, My uncle [2] and aunt in the country is well, and the [sic] are all well in town. I herd By Misses McMury [3] that my Mama was complaining about her head But I hope it is Bet Better. Give my love to all my friends and remember me to Joseph Donaldson [4] .

Give my love to Mama Bess [5] & Sally [6]

and remain

Your affectionate brother,

David Jackson [7]

PS Please send word when the ass has a foal, and tell my mama not to let the men put a bit in to [?] its mouth, give my love to the Boys and girls

Adieu Adieu.