Isaac Funk (November 17, 1797 – January 29, 1865) was an American rancher and politician, originally from Kentucky.

He was elected to the Illinois House of Representatives in 1840, ostensibly as a Whig, serving one two-year term.

In 1862, Funk was appointed to fill the Illinois Senate term of Richard J. Oglesby, who resigned to fight in the Civil War.

Isaac Funk, along with his attorney and friend, Abraham Lincoln, were responsible for bringing the Chicago & Alton Railroad through the Bloomington area, sidetracking it from its planned route through Peoria.

He fell ill with erysipelas and diphtheria the previous day at his home after returning from a legislative session.

Although he left no formal will and testament, his children donated $10,000 to create the Isaac Funk Professorship of Agriculture at Illinois Wesleyan.

His eldest son George Washington assumed most of his business interests and was later elected to the Illinois House.

He was the father of Eugene Funk, a prominent businessman and member of the Illinois Board of Agricultural Advisors.

Seventh son, Benjamin F. Funk, was elected to the United States House of Representatives.