You have to be very careful interpreting results from Google Ngrams and Google Books. The date they list for serials is usually the date the series was first published. You need to dig deeper to find the actual publication date for the particular issue. The publication dates they list for books are often wrong. You need to verify dates by looking at the publication data that is often printed in the first few pages.
For example, the “Corn Belt Council” reference above is from United States Congressional Serial Set. The series was first published in 1817, but the issue that the phrase appears in is volume 11687. I haven’t been able to track down an exact publication date, but it seems to be from about 1952.