[6] In 1904, Reinberg made his political debut by successfully running as the Democratic nominee for Chicago City Council in the 26th district.

[2] While Reinberg had originally indicated he would retire from the position, he made himself a candidate for another term in January 1914, as Mayor Carter Harrison IV had convinced him to stay aboard so that the board would continue to be led by an ally of superintendent Ella Flagg Young.

[18] Reinberg led McCormick (the county's leading Progressive Party politician) by more than a 60,000 plurality in the November election.

However, unlike in Reinberg's race, for the other countywide offices, Democratic nominees had only won by mere hundreds of votes.

[1][5] He was reelected in November 1918, defeating Republican Charles N. Goodlow by a much narrower margin than his victory four years prior.

Amid this, he ordered the Cook County Hospital closed to all visitors, except those visiting individuals dying from diseases other than the flu.

[23] After his death, the Forest Preserve District of Cook County would name a campground north of Palatine, Illinois "Camp Reinberg" after him.