Solon Mills is an unincorporated community and census-designated place in McHenry County, Illinois, United States. Solon Mills is located on U.S. Route 12, 2 miles (3.2 km) southwest of Spring Grove. Solon Mills is part of ZIP code 60071; it once had its own post office with ZIP code 60080 before it closed on September 28, 2002. It was named a CDP before the 2020 census, at which time it had a population of 133.

Historical population

Census	Pop.	Note	%±
2020	133		—
U.S. Decennial Census 2020

Solon Mills, Illinois first appeared as a census designated place in the 2020 U.S. Census.

Solon Mills CDP, Illinois – Racial and ethnic composition
Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.

Race / Ethnicity (NH = Non-Hispanic)	Pop 2020	% 2020
White alone (NH)	111	83.46%
Black or African American alone (NH)	0	0.00%
Native American or Alaska Native alone (NH)	1	0.75%
Asian alone (NH)	0	0.00%
Pacific Islander alone (NH)	0	0.00%
Some Other Race alone (NH)	0	0.00%
Mixed Race or Multi-Racial (NH)	10	7.52%
Hispanic or Latino (any race)	11	8.27%
Total	133	100.00%