A female friend of McKinley reportedly found the body after returning from an errand with his child. The sheriff declined to say if authorities found a suicide note.
"It's still part of our investigation and probably nothing we'll talk about right now," Robinson said.
"Everyone with the Broncos is shocked and saddened by the loss of Kenny McKinley," Broncos owner Pat Bowlen said in a statement. "He was part of the Broncos' family and will be greatly missed by our organization. My most heartfelt condolences go out to Kenny's family and friends."
The Broncos said coach Josh McDaniels would meet with the media on Tuesday.
In a statement, McDaniels said: "Kenny had a promising future on the football field, but more importantly, he was a great teammate whose smile and personality could light up the room. This is a tragic loss for our football team, and his family is in all of our thoughts and prayers during this difficult time."
McKinley's death is the latest in a series for tragedies for the Broncos in recent years. Cornerback Darrent Williams was slain in a drive-by shooting on New Year's Day 2007 and three months later backup running back Damien Nash collapsed and died after a charity basketball game in St. Louis.
McKinley was a second-year pro who was on the team's injured reserve list. He played in eight games as a rookie in 2009 with seven kick returns for 158 yards before going on injured reserve with a left knee injury on Dec. 29.
He recovered and participated in the team's offseason workouts but got hurt again during the first week of training camp and was placed on IR with a different left knee injury on Aug. 5.
McKinley was a fifth-round draft choice out of South Carolina in 2009. He attended South Cobb High School in Austell, Ga.
McKinley remains South Carolina's all-time leading receiver with 207 catches for 2,781 yards. He came back to the school earlier this month, watched the Gamecocks beat Georgia 17-6 and visited with his college coach, Steve Spurrier.
The Associated Press contributed to this report.