The county's rate of daily new COVID-19 cases is at 2.6 per 100,000 residents. That number would have to drop below 2 to join the yellow tier.
Last week it was at 1.7, but the county needs to meet yellow tier criteria for two consecutive weeks in order to move.
MAP: CA counties that can, can't reopen under new rules
The county attributes the rise in coronavirus cases to spring break travel.
"When a small uptick in cases is enough to keep us where we are, it's a sign we're not ready," health officer Dr. Matt Willis said in a press release.
Because of the recent rise in cases, the soonest Marin can join the yellow tier is May 4.
Had Marin joined the yellow tier, it would have meant loosened restrictions on businesses and social gatherings. One big change: bars that don't serve food would have been allowed to reopen indoors at 25% capacity -- a first in over a year for many businesses.
"I'm very excited about going inside at this point," Isaac Shumway, owner of bar California Gold in San Rafael, told ABC7 News Monday.
But not every Marin resident seems quite as excited to take that step.
RELATED: Marin Co. opens new drive-thru vaccination site with goal of 2,000 shots per day
"We were kind of surprised how limited people's desire to come inside was," Shumway said.
"You know people get close to each other in a bar," said Denisha Brekke of San Rafael. "I'm not going to lie, there's still a little anxiety looming over."
Marin County has one of the highest vaccination rates in the state. About 75% of the over-16 population has received at least one dose.
The yellow tier would also allow gyms to go from 25% to 50% capacity indoors. The owner of Body Kinetics in Mill Valley said he doesn't need the yellow tier numbers -- he isn't even reaching capacity in the orange tier.
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