The Pawtuxet Post Office, (Cranston Township, Providence County) was established on December 6, 1806 under Postmaster John A. Aborn. The Post Office was disestablished on October 31, 1900 and mail is currently handled by the Providence Post Office. 

George Francis Arnold was born in Cranston, Rhode Island in 1848 and is listed as a librarian's assistant on the 1880 Cambridge, Massachusetts Census. I could find no record for Sarah, who was evidently a relative as George's wife is listed as Tiza Arnold.

The complete text of the message follows below:

4 P.M. Wedn Letter from Mrs. Hill, atkins enclose tomorrow. a.
up to dinner. Very quiet since. L. best night for long time. I to
Fair tonight with Jennie. M. and Halls probably tomorrow
night. GP. M. We are nearly ready, Jennie, to walk down to
the Fair. I shall come home early and leave Jennie a ticket,
if she wants to stay an hour longer.  Thursday 8^1/2 a.m. I got
home at 9.30, and Jennie at 10.30. There was a good number
present, considering the rain. We both rode down and up, down
together, and up separate. The festival was quite a success and
will be more so, I hope tonight -- Allin slept well through the
night, and seems calmer and less feverish than yesterday. A
good change in the temperature 32^o - Albert