Bruce,
Although you requested info about U.S 4-4-0's active after WWII, Canadian locomotives were, for the most part, the same as U.S ones. Up here, CP Rail (Canadian Pacific) stabled a trio of 4-4-0's into the late '50's, and a couple of them were still around in 1960. All three are preserved: one at CP headquarters in Calgary Alberta, one at the Can. Rail. Historical Mus. at Delson Quebec, and one at the South Simcoe Railway at Tottenham Ontario. The one at Tottenham is receiving a new boiler, I believe, and should be running again in the not-too-distant future.
There is also one other - a former Canadian Pacific one, at Winnipeg Manitoba. It was recently rebuilt, completely, with a new boiler, and runs each weekend on its own right-of-way (a former Canadian National line) out of north-west Winnipeg. Go to "Prairie Dog Central" website for more info about it.
Hope this is of interest to you,
George