Yes, Sheriff's are part of the executive branch of government.
executive
The Executive Branch.
The secretary of defense goes under the executive branch. The president is the one that elects officers of the executive branch.
Unless the intention is to distinguish between Sheriffs, Mayors, and Governors, the question answers itself.
executive branch
executive
Executive.
The CIA is part of the executive branch.
executive branch
What is under the cabinet members that are part of the executive branch of your government?
The National Security Council is under the executive branch of government.
The IRS (Internal Revenue Service) is under the US Department of the Treasury, in the Executive Branch.