A method of forming a post sleeve within a post hole in the ground to include a post receiving cavity to insertably receive and support a post is provided. The method includes positioning a post sleeve core within the post hole with the aid of an elongate installation member and depositing uncured material into the post hole to at least partially surround the post sleeve core while the post sleeve core is attached to the elongate installation member. The method further includes allowing the uncured material to harden around the post sleeve core to form at least a portion of the post-receiving cavity of the post sleeve and removing the post sleeve core from the hardened material to expose the post receiving cavity to receive and support the post. Other related methods of forming post sleeves are also provided.