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There is no indication of the source. By the look of the 1846 article, the tables for other House elections have come from the same source, and have been imported wholesale into articles for the relevant dates.
I would like to know the source for my own selfish purposes! For instance, in this era (before a common election date in Congressional elections), it's vital to know the date of the elections in each state to understand the context in which that state's electors cast their ballots. And that information is not readily available in free online form; for example, the election results table in Congressional database available on this page gives the year but not the day or month of each election.