I'm wondering if this is a pickleweed mouse? It was found in the marsh where pickleweed is abundant.

Length: approx. 4 inches (9 cm) head to tip of tail (length of my index finger). Tail was approx. as long as the body.

Tip of tail was feathery. White fur on belly. Grayish brown fur on head and back.

Reference:
https://en.wikipedia.org/wiki/Salt_marsh_harvest_mouse