Of course which films one classifies as 'noir' is part of how one looks at this.
The Book Film Noir 2nd edition (Ward \ Silver), has 3 noir films listed for both 1958 and 1959.
1958 - The Lineup, Party Girl, and Touch of Evil
1959 - The Beat Generation, The Crimson Kimono, and Odds Against Tomorrow
(with none for 1960 and 2 for 1961 - Blast of Silence and Underworld USA).
There are 10 films listed for 1957 - Baby Face Nelson, The Brother Rico, The Burglar, Crime of Passion, The Garment Jungle, The Night Runner, Nightfall, Plunder Road, Sweet Smell of Success, and The Tattered Dress.
My point being that the list cigarjoe provided of B&W noir films and the listings above, 'match' in that there is a major drop off of noir films after 1957.
Also, the only noir icon that made significant noir films after 1959 is Mitchum with Cape Fear (1962), The Friends of Eddie Coyle and Farewell my Lovey.
Is that another reason to site 1959 as the end of an era?
I would include a few others along with Mitchum
Here is a list of some B&W Noirs (there may be a few more) after 1959 some with Noir Icons and most with Noir actors, others are really low budget or in the case of Sam Fuller's post 1960 films populated with a lot of TV actors.
1960 -1968 B&W Noir (at least as I see them, The Money Trap (1965) with Glenn Ford, Rita Hayworth, Ricardo Montalban, may be another but I've only seen clips
Psycho (1960) Janet Leigh (Act Of Violence - Touch of Evil) John McIntire
Blast Of Silence (1961) v.o. Lionel Stander (Hangmen Also Die! -Call Northside 777 )
Underworld U.S.A. (1961) dir Sam Fuller
Something Wild (1961) Ralph Meeker (Kiss Me Deadly)
Cape Fear (1962) Robert Mitchum
Experiment In Terror (1962) Glenn Ford
Satan in High Heels (1962) Meg Myles (The Phenix City Story - New York Confidential )
The Manchurian Candidate (1962) Frank Sinatra (Suddenly - The Man with the Golden Arm )
Shock Corridor (1962) dir Sam Fuller
Requiem for a Heavyweight (1962) Anthony Quinn (The Long Wait, The Naked Street)
The Naked Kiss (1964) dir Sam Fuller
The Pawnbroker (1964) Rod Steiger (The Big Knife -The Harder They Fall - Cry Terror! ) Juano Hernandez (The Breaking Point -Kiss Me Deadly)
The Glass Cage (1964) Elisha Cook Jr.
Angel's Flight (1965) low budget
Brainstorm (1965) Jeffry Hunter (Fourteen Hours) Dana Andrews, Viveca Lindfors, Strother Martin
Once A Thief (1965) Jack Palance, Van Heflin
Aroused (1966) low budget
Mr. Buddwing (1966) Jean Simmons (Angel Face)
In Cold Blood (1967) Paul Stewart, Jeff Corey, Charles McGraw
The Incident (1967) Thelma Ritter, Jan Sterling, Gary Merrill
The Pick-Up (1968) low budget