Forty two years counting spots: Solar observations by D.E. Hadden during 1890–1931 revisited

•We made a compilation of solar observations made by D.E. Hadden during 1890–1931.•The vast majority of these observations were not previously compiled.•We show the solar sources of two of the major storms recorded in the past.

We have recovered the sunspot observations made by David E. Hadden during 1890–1931 from Alta, Iowa. We have digitized the available data published by Hadden in different astronomical journals. This data series have been analyzed and compared with the standard sunspot number series. Moreover, we provide additional information on two great sunspot groups, previously not described, that originated two important extreme episodes of space weather on February 1892 and September 1898.