Pi Beta Phi was founded on April 28, 1867 in the home of "Major" Jacob Holt (he really wasn't a major, but he had previously worked at West Point and picked up the nickname). The southwest upstairs bedroom was rented by Ada Bruen and Libbie Brooks while they attended Monmouth College (this was in the days before the college had dormitories). Pi Beta Phi was founded as I.C. Sorosis; Pi Beta Phi was its Greek motto. It was fashioned after the men's fraternities at Monmouth.
In the late 1930s, the home came into Pi Beta Phi's hands when it was purchased by a Pi Phi's dad at a delinquent tax auction. In the early 1940s, it opened as a memorial to Pi Beta Phi's founders.
Kappa owns and maintains the Stewart House in Monmouth. The bridge and creek are no longer there.
Alpha Xi Delta was founded at Lombard College in Galesburg, Illinois. It closed. The site of the college is now occupied by Lombard Middle School. The archives from the college were given to the library at Knox College (also in Galesburg).
Kappa Delta doesn't really have a single room or spot at Longwood University that we identify as our founding location. We do have a bench on campus that is called the Founders' Bench, but it's a memorial, not the original spot. All 4 of the Farmville Four are also memorialized on the Founders' clock.