Primary sources can be found anywhere. You are a primary source.
Example #1
George L. White letter, 1861
Written by George L. White to "Mr. Stevens" on October 3, 1861, from Washington, D.C.
In the letter, White states that seven men in his regiment have died in Baltimore, including a William Knowlen (Noland?) from No 11 Aroostook." He was buried in the western cemetery of the city. he mentions their skirmishes under the direction of Generals McLellan and Scott and describes fighting the Confederate forces. He also mentions the 8th, 9th, and 10th Maine. White states that the weather is as cold in Baltmiore as it was in Fort Kent at that time the previous year.
Acadian Archives/Archives acadiennes collection MCC-00222
Example #2
Pierre A. Cyr ledger, 1905-1907
This collection consists of a business ledger belonging to Pierre A. Cyr, spanning the years 1905-1907. The primcipal business contained in the ledger is for a potato broker and shipper.
This ledger is both a primary and a secondary source:
Within the first 15 pages of the ledger are interleaved 12 pages of description for both the ledger and the Cyr family, written by Guy Dubay in 2006.
Acadian Archives/Archives acadiennes collection MCC-00305
Example #3
Census
A timeline of census taking in the United States: