The main campus of the University of Redlands is in Redlands, CA, which is about 70 miles east of downtown Los Angeles. For a map, click here.
There a number of airports serving the greater Los Angeles area. For a list, click here (missing from that list is the Palm Springs airport, which is 47 miles from the Redlands campus)
The Ontario International Airport (ONT) is closest, roughly 25 miles to campus). Although Los Angeles International Airport (LAX) is farther, at 84 miles, it may be the most feasible for those who who are coming from other coutries.
Because the University has its own train station, it is possible (with some planning) to get to the University from either LAX and ONT via bus and train (see, e.g., this link provides information about getting to a Metrolink station from the ONT airport).