pari-mutuel or "Paris Mutual"

These dates are focused on harness racing.
Some of the dates may by mere mentions, rather than implementation.

Anybody have more to add?

Excerpt from Dec 1949 Hoof Beats article by John W. Paten
Pari-Mutuel (or Paris Mutual) is a form or method of wagering (1) or
investing (2) wherein two or more persons place monies in a common fund or
pool and the participation of one or more of them, is eliminated at the
finish of a contest. A contest may be any type of competition which lends
itself to practical application of pari-mutuel operations.
Pari-mutuel was originated by Pierre Oller, a Frenchman, about 1865. His
first operation was within the city of Paris during 1872. It quickly proved
its utility and practability to Parisians,-particularly those who desired to
conserve their time, energy and the attendant cost of going to the track.
A definition and description of the word Mutuel (French) or Mutual
(American) may be of interest. Either word means an equal interest invested
in two or more persons, or an interest "between themselves", herein it
relates to a fund or pool. Of course, after the official finish of a contest
only those holding similar winning tickets have a "between themselves"
interest in the return of the amounts they wagered or invested and a
proportionate share of the surplus or profit.
It is said that Pierre Oller originated "Pari-Mutuels" to overcome the
surreptitious activities of bookmakers and of course, with the incentive of
producing revenue therefrom. In the beginning blocks of prenumbered tickets
were used. Each block represented an entry in a particular race. Tickets
were sold on each entry and the first three finish positions, namely, first,
second and third-in racing parlance, Straight, Place and Show. The aggregate
fund or pool was obtained by a manual tally of all the tickets sold. When
the results of a race became known, the tickets on the first three to finish
were likewise manually tallied in order to determine the remaining surplus
or profit mutually or equally belonging to the holders of the winning
tickets.

1935 Maine

1936 A new Pari-Mutuel betting was installed at the San Joaquin County Fair
(California) on Saturday (no betting allowed Sunday) for the six running
races, which made the total betting for the seven days of the meeting
$108,244. The largest pay-off was in the 2:24 trot on August 29 when Jean
Morris paid $180.40 for place in the second heat. There had only been one
$1.00 ticket sold on the mare.
Also at Pomona (Los Angeles County Fair)

1936 Rhode Island,

1937 possibly Canada; via the efforts of George McCall.

1938 Ohio (Berea)

1940 NY; "the number of pari-mutuel plants in operation" (specific mention
of Saratoga), another mention of Roosevelt. Batavia opens.

1944 Freehold

1944 Northbille Downs track opened in 1944 when Northville pioneered
pari-mutuel harness racing in the midwest.

Mass 1947 (night pari-mutuel)
Holllywood Park 1947

Maryland 1948 (per Ed Keller) ; Laurel Raceway, the track which pioneered
pari-mutuel harness racing in this area 10 years ago (from a 1958 article)

1959 Rochester, N. H., the first fair in the nation to present pari-mutuel
racing (not so; see California 1936 and Ohio 1938)

1959 Ponce De Leon only Fla harness racing

Robert Bomar (1908-81) was one of the first black horsemen to drive at any
pari-mutuel track and was generally regarded as probably the first black to
drive at any western New York track. (online obit)