SH2 204 taken from my Creedmoor site on October 12th and 13th.
Avedisova says that Sh 2-204 is likely ionised by four O-class stars that are part of the Cam OB3 association. These are BD +56 864 (O6 V), HD 24372 (O9.5 Ib), Hiltner 52 (O7.5 V) and BD +56 866 (O9 V).

The distance estimates from Avedisova and Russeil both place this nebula beyond the Perseus arm and possibly associate it with the Norma/Outer arm.
However, a 2005 study connects Sh 2-204 to the much closer Cam OB1 association.