The 22/220 Illini is one of the most reliable bus lines offered by the Champaign-Urbana Mass Transit District.
It services bus stops between the off-campus Lincoln & Killarney to PAR, visiting other important stops such as the ARC, Illini Union, Gregory at Library and ISR along the way.
The 22 runs on weekdays from 6:21 a.m. to 7:20 p.m., at which point it becomes the 220 Evening and continues service until 5:10 a.m. The 22 does not run on the weekends and is only run as the 220.
There is also an Illini Limited version of both the 22/220 that goes from Lincoln & Killarney to the ARC and back. This limited line runs on the weekends in place of the 22 as well. Due to the proximity of the 22/220 to almost all residence halls, it is quite a popular choice for on-campus travel despite being one of the longer routes.
While you might come across memes warning against the evils of getting on the 22, you will be hard-pressed to find a line that has stops in such proximity to that many campus hotspots operating reliably almost 24/7.