Dear Mr. Bettenhausen,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series Reports of Site Locations, 1837 - 1950 in the Records of the Post Office Department (Record Group 28) that includes 2 files for Cook County Illinois. These records have been digitized and are available using the Catalog. We also located the series Letters Sent, 10/3/1789 - 12/31/1952 in Record Group 28 that may contain a reference to the name change of New Bremen Post Office in 1890. For access to the non-digitized records, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at firstname.lastname@example.org.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
We hope this is helpful. Best of luck with your research!