Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Placid

Placid as a duck pond.
—Anonymous

Placid as a mill-pond.
—Anonymous

Placid as a scarecrow in a field of scoundrels.
—Anonymous

Placid as a soft-shell crab in a plate of parsley.
—Anonymous

Placid as Socrates.
—Anonymous

Placid as Paradise.
—Edwin Arnold

Placid as a hearthstone.
—Eugene Field

Placid as a stone.
—Victor Hugo

Placidly … as waiting to be sheeted home.
—Jean Ingelow

Placid as a swan that drifts in a dream.
—James Russell Lowell