Here’s an interesting clipping from The News and Herald (South Carolina), 1881:
The concept lasted a while, and there are several stories floating around about bullfrogs being tossed into butter churns by reluctant children eager to avoid their chores. Here’s another clipping from 1955 about a boy who thought it’d be clever to use the idea in a butter churning contest:
He may have been disqualified, but it’s clear the story delighted many: this exact article can be found in newspapers in Montana, Kansas, Ohio, New York, and Texas, along with several others.
And here’s another clipping from 1977 about the story of the bullfrog in the buttermilk:
Try a search on Newspapers.com for more on this topic or any other you like. The browse pages are also helpful for perusing the pages of time gone by.