Leonard, 26, becomes the club's first new signing and joins from Mossley.
He has impressed in pre-season so far, scoring a free-kick away at Radcliffe in the Rams’ most recent friendly fixture.
The striker progressed through the ranks at Huddersfield Town before playing non-league football locally at AFC Emley, where he hit the headlines after scoring 42 goals in the 12/13 season.
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