The airline was making arrangements to fly the passengers to New Jersey on another plane.
The Dallas-based airline also made a point to say this did not qualify as an "emergency landing".
Southwest officials said there was no loss of pressurisation in the plane's cabin, noting that windows on the aircraft have "multiple panes".
While the two events sound similar at face value-both involved window damage mid-air followed by an unexpected landing-it is still unknown what caused today's incident.
Passenger Alejandro Aguina said on Twitter the crack was located on the "outside" of the plane. "All of a sudden, we heard an explosion and I come to find out that the engine exploded on the left side of the plane". The airline was trying to make arrangements to get the 76 passengers to Newark on another plane.
Photographs taken by a passenger on Southwest Airlines flight WN957, which took off from Chicago Midway International, show a broken window next to a row of passenger seats.
The Boeing 737-700 was on its way to Dallas from New York City, but made an emergency landing in Philadelphia about 40 minutes into the flight, according to CNN. The second plane landed only an hour later than the flight was originally supposed to land. Engine debris was found about 70 miles away from Philadelphia.
It added: 'The flight landed uneventfully in Cleveland.
This is the latest in several incidents involving Southwest Airlines flights.
A witness told website DansDeals.com that some people were crying hysterically, while the crew acted very professionally.
Anthony Roman, a commercial pilot and flight instructor based in NY, says problems with windows should be detected during regular inspections and maintenance. Despite receiving CPR and electric shocks to the heart, Riordan later died from her injuries.