Dear Kerkko Kuha,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the Population Schedules for the 1930 Census, and the Population Schedules for the 1940 Census in the Records of the Bureau of the Census (Record Group 29) that may contain information about Harald Karlsson. The 1940 Census schedules are digitized and available using the Catalog. For more information about the non-digitized schedules, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at email@example.com.
We also located the Index to Alien Arrivals at Canadian Atlantic and Pacific Seaports, 1909 - 1940 in the Records of the Immigration and Naturalization Service (Record Group 85) that include a Harald Karlsson, age 35, born about 1890, arrived in the USA in 1925. Please contact RDT1 for more information.
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.
The Statue of Liberty—Ellis Island Foundation, Inc has an online searchable database of 22.5 million arrivals to New York between 1892 - 1924 that includes several persons with the name Harald Karlsson arriving from Finland or Sweden.
We suggest that you review NARA’s Resources for Genealogists, as well as the document Suggestions and Advice for Family History Researchers may be useful.
Lastly, please contact the National Archives of Finland for information about any records in their custody about Harald Waldemar Karlsson and search the Finland Emigration and Immigration website for any resources and/or other information about his departure from Finland and the countries where he later arrived.
We hope this is helpful. Best of luck with your family research!