July 3rd, 1890. All of the dates are days states were admitted into the Union (in order: Iowa, Delaware, Alabama, Hawaii, and Oregon). The first letter of each state spells out IDAHO, which was admitted to the Union on July 3rd, 1890.
Quick solve 'sonofapollo' . congratulations, yes, you solved first the connection with the States and secondly the spelling of Idaho from first letters....... Your 4th Challenge Solve .... your Honorary Gold Medal is on its way :o)