Site Selection for the 1941 Worldcon was conducted at Chicon I, the 1940 Worldcon. The process was still very rudimentary and the bidders were not really yet organized into bids. The decision was probably made by a show of hands at some point duringt he convention.
There apparently were two somewhat "formal" bidders: Denver in 1941 (which won the right to host the 1941 Worldcon as Denvention I) and a New York in 1941 bid about which we know little except that they did not lose gracefully. Additionally, there were fans from Chicago who wanted to do it again, and fans from Cleveland who were interested.
The New York in 1941 bidders planned to hold the convention in Newark. They felt that Denver was too far away and decided to hold their convention anyway. There was much feuding in the fan press, which ended only after Ray Palmer, SF editor for Ziff-Davis through his support behind Denver.