Hinrichsen became involved with the Democratic Party in 1888, eventually rising to the position of Secretary of State of Illinois in 1892.

[1] Hinrichsen was appointed Deputy Sheriff of Morgan County in 1874 and served three two-year terms in that position, residing at Jacksonville.

Hinrichsen returned to Jacksonville after selling the Herald in 1890 and was elected Clerk of the House of Representatives of Illinois the next year.

Hinrichsen was nominated as the Democratic candidate for Secretary of State of Illinois in 1892 and was elected to a four-year term under John Peter Altgeld.

Hinrichsen was nominated by his party to the United States House of Representatives in 1896 and won the election.

He managed the Cincinnati Enquirer for a year while its Democratic editor John Roll McLean sought the governorship of Ohio in 1899.

The next year, he was Traveling Manager of the Democratic National Committee, raising funds for the 1900 presidential campaign.