Updated: Dec 17, 2022
This cover is likely from the early 1850s. I assume that is the case because this envelope has two stamps that help narrow the timeframe.
In the upper-right corner of Figure 1 is a 3-cent stamp that paid the postage for this letter to travel from Philadelphia to Vincennes, Indiana. That stamp is #10A in the US Scott Catalog and was in use between 1851 and 1857. It is tied to the envelope with a blue "Philadelphia PA" cancellation, but the day and year are illegible.
The other stamp, in the upper-left corner, is a 1-cent Blood's Dispatch stamp, which was first issued in 1850. You can see that stamp better in the close-up in Figure 2. This is #15L13 in the US Scott Catalog.
The "L" in the catalog number stands for "local." Blood's Dispatch was based in Philadelphia and for a fee - 1-cent in this case - it would carry a letter from a local home or business to a post office so the item could enter the US postal system. These local carriers could be found in cities throughout the US - Boston, Chicago, New York, Cincinnati, etc. - and before 1845 would actually delivery mail between cities. You can read about one such item in my collection here.
The Blood's Dispatch stamp is "acid tied" to the cover. That discolored the stamp and showed that it had been used. There is also a circular date stamp showing that Blood's Dispatch picked up this item sometime in the afternoon of October 29, year unknown.
There is no indication on the cover of who sent it nor is there any enclosure to provide a clue.
The letter was sent to a James H. Roberts of Vincennes, Indiana. That town is about 130 miles southwest of Indianapolis.
I haven't been able to definitely identify Mr. Roberts. A possible candidate is a "J.H. Roberts" who was living in Vincennes in 1850 per that year's census. This person was born in Illinois between 1826 and 1830 (it's hard to make out his age; he was either 20 or 24) and is listed in the 1850 census with the occupation "attorney." The household in which he was living does not appear to be a relation. By 1860, a person by the name of "Jas. H. Roberts" - born in Illinois in 1830 and working as a "lawyer" - was residing in Chicago (according to the census records).
A little more digging on Ancestry.com turned up a lawyer by the name of James Henry Roberts who was born in Kaskaskia, Illinois (near St. Louis) in 1825. According to his obituary, he arrived in Chicago in 1856, but it doesn't say from where. Interestingly, his mother - Susan nee Lamb - was born in Chester, Pennsylvania, which is just south of Philadelphia. James Henry Roberts had a successful legal career in Chicago and died at the ripe old age of 95 in 1920 in Philadelphia where he was visiting his daughter.
I acquired this cover with five others at a Dutch Country Auction held on November 15-17, 2022. The total purchase price was $345.00 (including a 15% buyer's premium), or $57.50 per cover. This item has a catalog value of $1,000.00.
Figure 2 - Close-up of Blood's Dispatch Local Stamp US Scott Catalog #15L13
Figure 3 - Back of envelope